VANCE, Circuit Judge:

In this case we are asked to decide whether the district court properly abstained from hearing a case brought before it under section 306 of the Railroad Revitalization and Regulatory Reform Act of 1976, Pub.L. No. 94-210, 90 Stat. 31, 54 (1976) (codified with some differences in language at 49 U.S.C. § 11503) (the 4R Act or the Act). That provision prohibits a state or subdivision thereof from assessing rail transportation property at a value that has a higher ratio to the true market value of that property than does the assessed value of other commercial and industrial property in the state or subdivision. Section 11503 of the codified 4R Act also makes it unlawful to levy or collect taxes on rail property assessed in this discriminatory manner. The section confers concurrent jurisdiction on federal district courts to enforce its provisions.

I. Preliminary Matters.

The private appellants in this case are nine interstate rail carriers (the railroads) owning property in the state of Georgia. Relying on a sales ratio study prepared by the Georgia Department of Audits which showed that, in the aggregate, local nonrailroad property in many Georgia counties in 1979 was preferentially assessed at a value far below the forty percent of fair market value required by state law the railroads brought this action in federal district court to enjoin the issuance by the Georgia State Board of Equalization (the state board) of an order which allegedly would result in the assessment of their property in a discriminatory manner.

Prior to bringing this suit the railroads appealed their proposed assessments for 1979 to the state board under the procedure Georgia provides for that purpose. See Ga. Code Ann. § 48-2-18 (1982), amended by § 48-2-18 (Supp. 1983); Ga. Code Ann. § 48-2-46 (1982). The designated hearing examiner rejected claims made by some of the railroads that their property was valued far in excess of its true market value but found on the basis of the sales ratio study that many counties discriminatorily assessed local nonrailroad property below the forty percent of true market value required by law. As a consequence, the examiner recommended that the assessment percentages applied to each railroad's system value be reduced correspondingly in those counties.

On April 15, 1981, in summary fashion, the state board approved and accepted all recommendations of the examiner except those which would eliminate the disparity between locally assessed property and rail property in the counties where the ratio study showed locally assessed property to be undervalued. The board gave no reasons for this rejection but implicitly ruled that, despite the significant discrepancies evidenced by the sales ratio study, the county assessments were "reasonably uniform" under Georgia law. After the board announced its decision but before it could issue an order the railroads filed this action. The district court's subsequent restraining orders and injunctions continue to prevent the board from issuing its order assessing the railroads property taxes.

II. Property Tax Assessment in the State of Georgia.

The Georgia state revenue commissioner assesses utilities including railroads centrally. See Ga. Code Ann. §§ 48-5-510 through -524 (1982). Other commercial and industrial property is assessed by the county in which it is located. These local assessments are performed by the various county boards of tax assessors. See Ga. Code Ann. §§ 485-5-290 through -313 (1982 Supp. 1983). The state revenue commissioner by law must require all counties to assess property uniformly. Hawes v. Conner, 224 Ga. 567, 163 S.E.2d 724, 726 (1968). The degree of uniformity required is styled "reasonable uniformity." See Strickland v. Douglas County, 246 Ga. 640, 272 S.E.2d 340, 342 (1980). The commissioner's decision that assessments within a given county should be increased, decreased or left unchanged must be upheld by reviewing courts unless the action is "unreasonable, beyond his authority or constitute an abuse of discretion." Id.

III. Protections Afforded Railroads by the 4R Act.

Section 11503 grants federal courts concurrent jurisdiction to impose sanctions once a railroad shows that the ratio of assessed value to true market value of its property exceeds by at least five percent the assessed value to true market value of other commercial and industrial property within the taxing jurisdiction. Once this five percent jurisdictional threshold has been met the Act requires the court to enjoin the assessment of discriminatory taxes in any amount. The district court has explicit jurisdiction to issue injunctive relief notwithstanding the Tax Injunction Act of 1937, 28 U.S.C. § 1341.

IV. The Case Below.

The district court observed that Georgia law requires uniform valuations of all property and described in detail Georgia's appellate procedure in property tax cases. The court then distinguished this situation from 4R Act cases involving de jure discrimination, observing that "there is no conflict between the Georgia Revenue Code and section 306." The court further noted that "any contention by the railroads that the State Board of Equalization misapplied either federal or state law as such law relates to the tax structure imposed on the railroads would be without merit, since state law requires, and the State Board of Equalization so recognized, that uniformity of taxation is required."

After noting that the state board had considered state and federal directives "that railroad property must be treated equally with commercial and other industrial property," the court observed that the railroads' complaint did not allege "any sinister plot on the part of the State Department of Revenue to circumvent either section 306 or the Georgia statutes by purposefully valuing their properties at a value higher than the actual true market value; the complaint merely alleges that the valuations and resulting assessments are incorrect. Thus narrowed, the focus of the railroads' complaint is whether the valuation placed upon their property is, indeed, the fair market value."

The district court concluded that abstention was proper under Burford v. Sun Oil Co., 319 U.S. 315, 63 S.Ct. 1098, 87 L.Ed. 1424 (1943). It justified restraint by noting that federal intervention could disrupt effectuation of the state policy of uniform taxation which in this case parallels federal law. The state's special expertise in valuation and assessment, the matter at hand, was also of relevance. The court added as a third reason for its abstention "the fact that protracted litigation could result because . . . the remedy which this court can provide is severely limited."

V. The Appeal. [15] A. Burford abstention in general.

"`The doctrine of abstention, under which a District Court may decline to exercise or postpone the exercise of its jurisdiction, is an extraordinary and narrow exception to the duty of a District Court to adjudicate a controversy properly before it.' " Colorado River Water Conservation District v. United States, 424 U.S. 800, 813, 96 S.Ct. 1236, 1244, 47 L.Ed.2d 483 (1976) (quoting County of Allegheny v. Frank Mashuda Co., 360 U.S. 185, 188-89, 79 S.Ct. 1060, 1062-63, 3 L.Ed.2d 1163 (1959)); accord Reetz v. Bozanich, 397 U.S. 82, 86, 90 S.Ct. 788, 790, 25 L.Ed.2d 68 (1970); Zwickler v. Koota, 389 U.S. 241, 248, 88 S.Ct. 391, 395, 19 L.Ed.2d 444 (1967); Baggett v. Bullitt, 377 U.S. 360, 375, 84 S.Ct. 1316, 1324, 12 L.Ed.2d 377 (1964).

Burford v. Sun Oil Co. and a group of arguably similar cases have been assembled into an uneasy category of abstention to which Burford lends its name. Although the contours of Burford-type abstention are ill-defined, the doctrine when applicable is invoked where the "exercise of federal review of the [state law] question in a case and in similar cases would be disruptive of state efforts to establish a coherent policy with respect to a matter of substantial public concern." Nasser v. City of Homewood, 671 F.2d 432, 439 (11th Cir. 1982) (quoting Colorado River, 424 U.S. at 814, 96 S.Ct. at 1244); see also BT Investment Managers, Inc. v. Lewis, 559 F.2d 950, 954-55 (5th Cir. 1977). Because Burford abstention results in the dismissal rather than stay of federal proceedings as well as in the "refusal to exercise federal jurisdiction in an entire class of cases, it is perhaps the most potent device in" the abstention area. Nasser v. City of Homewood, 671 F.2d at 440; BT Investment Managers, 559 F.2d at 955.

B. The propriety of abstention under the 4R Act.

Whether Burford should be applied to cover challenges by rail carriers to discriminatory state property tax assessments under section 11503 is a case of first impression in this circuit. The posture of the state and federal interests is significantly different in this case than in previous abstention cases. Because we decide that Congress meant unconditionally to ensure a federal forum for section 11503 claims, we conclude that the statute bars abstention in cases alleging de facto discrimination as well as de jure.

1. The continued vitality of equitable restraint in suits involving state taxes.

Both Congress and the federal courts have acknowledged that the ability to administer fiscal affairs via taxation free of interference from the federal judiciary is of primary importance to a state's economical well-being. Federal courts had long practiced abstention or its equivalent in deference to this state interest by the time Congress passed the Tax Injunction Act, 28 U.S.C. § 1341. See, e.g., Matthews v. Rodgers, 284 U.S. 521, 52 S.Ct. 217, 76 L.Ed. 447 (1932); First National Bank v. Board of Commissioners, 264 U.S. 450, 44 S.Ct. 385, 68 L.Ed. 784 (1924); Singer Sewing Machine Co. v. Benedict, 229 U.S. 481, 33 S.Ct. 942, 57 L.Ed. 1288 (1913); Boise Artesian Hot Cold Water Co. v. Boise City, 213 U.S. 276, 29 S.Ct. 426, 53 L.Ed. 796 (1909). The Tax Injunction Act was intended to codify this pre-existing federal equity practice and to ensure more uniform adherence to the underlying principles of comity by erecting a jurisdictional bar to supplement the existing equitable restraint. See generally United Gas Pipe Line Co. v. Whitman, 595 F.2d 323 (5th Cir. 1979).

The equitable doctrine has not been replaced by section 1341. Since enactment of the provision courts have applied an equitable policy of non-interference to suits involving state taxes when the suits are not specifically within section 1341. See, e.g., Fair Assessment in Real Estate Association v. McNary, 454 U.S. 100, 102 S.Ct. 177, 70 L.Ed.2d 271 (1981); Great Lakes Dredge Dock Co. v. Huffman, 319 U.S. 293, 63 S.Ct. 1070, 87 L.Ed. 1407 (1943); United Gas Pipe Line. The justification given by courts for refusing to hear state tax cases outside the literal scope of section 1341 involves a determination that congressional intent counsels the expansion followed by a decision that equitable restraint is appropriate under the circumstances. See California v. Grace Brethren Church, 457 U.S. 393, 412-13, 416-17, 102 S.Ct. 2498, 2510-11, 2512-13, 73 L.Ed.2d 93 (1982); Fair Assessment, 454 U.S. at 107 n. 4, 109-10, 102 S.Ct. at 181 n. 4, 182-83; Rosewell v. LaSalle National Bank, 450 U.S. 503, 522-27, 101 S.Ct. 1221, 1234-36, 67 L.Ed.2d 464 (1981); Great Lakes, 319 U.S. at 300-01, 63 S.Ct. at 1074; United Gas Pipe Line, 595 F.2d at 326.

2. The congressional guarantee of a federal forum for section 11503 suits.

Without doubt the well-being of the nation's railroads is essential to its economic health. In passing section 11503 Congress acted "to eliminate the long-standing burden on interstate commerce resulting from discriminatory State and local taxation of common and contract carrier transportation property." S.Rep. No. 630, 91st Cong., 1st Sess. 1 (1969).

In hearings on the provision Congress heard testimony from the National Association of Tax Administrators on behalf of the states to the effect that state court remedies were "adequate to deal effectively with assessment discrimination cases" and that state tax departments made "substantial progress in eliminating discrimination" and that federal injunctive relief would interfere with states' abilities to classify property to carry out state policies promoting better land use, location of industry, homestead tax relief and old age property tax relief. See S.Rep. No. 630 at 8. Nevertheless Congress determined that strong federal policies demanded a federal forum as well as a federal substantive remedy. Id. at 6-7. Congress realized that the Tax Injunction Act, which prohibits district courts from enjoining state taxing activity where state law provides a plain, speedy, and efficient remedy in the state's courts, had the undesirable effect of closing the doors of the federal courts to railroads affected by discriminatory taxation where the state's remedies were neither plain, speedy, nor efficient. S.Rep. No. 630 at 6-8; S.Rep. No. 1483, 90th Cong., 2d Sess. 6 (1968). Therefore Congress provided in section 11503 a specific exemption to the Tax Injunction Act.

The state board argues that, in states such as Georgia where de jure discrimination does not exist, state and national policies are aligned and the federal judiciary should require taxpayers to use the state's remedies. We do not agree. The legislative history and broad language of the Act show Congress possessed a general concern with discrimination in all of its guises. See S.Rep. No. 630 at 6 (favorably quoting S.Rep. No. 445, 87th Cong., 1st Sess. 466 (1961)); S.Rep. No. 630 at 15; S.Rep. No. 445 at 458.

Section 11503 suits differ from ordinary taxpayer suits in that the potential class of section 11503 plaintiffs is limited to rail carriers. Exercise of federal jurisdiction thus will not transform the district court into "`a source of appellate review of all state property tax classifications.'" Fair Assessment, 454 U.S. at 114, 102 S.Ct. at 185 (quoting Fair Assessment in Real Estate Association v. McNary, 478 F. Supp. 1231, 1234 (E.D.Mo. 1979)). There are, however, other concerns. A judicial appraisal of valuation techniques could well affect the state's choice of future assessment methods. Further, although the railroads are relatively few in number and tend to pool their litigation efforts their combined tax bill is substantial. "During the pendency of the federal suit the collection of revenue under the challenged law might be obstructed, with consequent damage to the State's budget. . . ." California v. Grace Brethren Church, 457 U.S. at 410, 102 S.Ct. at 2509 (quoting Perez v. Ledesma, 401 U.S. 82, 128 n. 17, 91 S.Ct. 674, 699 n. 17, 27 L.Ed.2d 701 (1971)). Litigation of section 11503 claims could also allow the railroads to "escape the ordinary procedural requirements imposed by state law." Id.

The extensive legislative history of the 4R Act and its numerous predecessor bills makes it clear that Congress thoroughly considered the effects the Act would have on state taxation policies and practices. After weighing these effects, Congress concluded that both a federal remedy and a federal forum were necessary to further the strong national policy of protecting interstate commerce from the disruptive effects of discriminatory state and local taxation of railroad property. See, e.g., S.Rep. No. 630 at 6-8; S.Rep. No. 1483 at 6. Congress provided for both solutions in the resulting law.

"[A] court should not defer the exercise of jurisdiction under a federal statute unless it is consistent with that intent." Patsy v. Board of Regents, 457 U.S. 496, 501-02, 102 S.Ct. 2557, 2560-61, 73 L.Ed.2d 172 (1982). The legislative history of section 11503 demonstrates that Congress intended to carve out an exception not only to the Tax Injunction Act, but also to the underlying doctrine of equitable restraint in the narrow area of discriminatory taxation of railroads. Congress meant to guarantee a federal forum for railroad suits, and only an exemption from abstention in all its forms would accomplish this purpose. Since Congress has spoken, it is not our province to alter the balance Congress struck in providing a federal forum for rail carrier claims of tax discrimination under section 11503.

Fair Assessment in Real Estate Association v. McNary, 454 U.S. 100, 102 S.Ct. 177, 70 L.Ed.2d 271 (1981), does not require a different result. In a suit for damages under section 1983 of the Civil Rights Act of 1871, 42 U.S.C. § 1983, taxpayers claimed that disparate assessment of their newly improved real property deprived them of equal protection and due process of law. Section 1983 ordinarily provides an immediate federal forum for citizens whose constitutional or federal rights allegedly have been denied by any state despite the presence of an adequate state forum. See McNeese v. Board of Education, 373 U.S. 668, 83 S.Ct. 1433, 10 L.Ed.2d 622 (1963); Monroe v. Pape, 365 U.S. 167, 81 S.Ct. 473, 5 L.Ed.2d 492 (1961). Viewing the case as a clash between "two divergent lines of [statutory] authority," 454 U.S. at 105, 102 S.Ct. at 180, the Supreme Court ruled that the principle of comity together with section 1341 require abstention in the face of jurisdiction under section 1983.

Section 11503 involves no such collision with the Tax Injunction Act. Its legislative history, unlike that of section 1983, evinces a congressional intent to exempt taxpayer plaintiffs from the Tax Injunction Act as well as from the comity principle. Further, because the economic due process claims in Fair Assessment fell at the extreme periphery of the concern behind section 1983, abstention in that context left the vital core of section 1983 protections intact. Abstention here, in contrast, would rob the jurisdictional grant of section 11503 of all meaning, since the railroad plaintiffs belong to the small class of direct beneficiaries contemplated by Congress and seek precisely the tax relief the section affords. Finally, the potential for wholesale federal litigation of state taxpayer claims, very real under section 1983, is nonexistent under section 11503.

Moe v. Confederated Salish Kootenai Tribes, 425 U.S. 463, 96 S.Ct. 1634, 48 L.Ed.2d 96 (1976), exemplifies an instance in which a jurisdictional statute properly took precedence over the equitable restraint doctrine and its statutory counterpart, section 1341. The Supreme Court gave effect to a district court decision enjoining Montana's collection of certain vendor licensing and sales taxes from Indian merchants. In deciding that abstention in the case was improper the Court relied on a jurisdictional statute, enacted ten years earlier, which reflected a congressional intent to provide Indian nations with a federal forum for certain civil actions. See 28 U.S.C. § 1362. Neither the statute nor its legislative history mentions any exemption from the Tax Injunction Act. The Court concluded however that the statute conferred jurisdiction despite the command of the Tax Injunction Act because the statute, as construed, extended to the tribes the common law exception to section 1341 which allows the United States and its instrumentalities to sue in federal court to complain of "unconstitutional state exactions." 425 U.S. at 470-74, 96 S.Ct. at 1639-42 (quoting Department of Employment v. United States, 385 U.S. 355, 358, 87 S.Ct. 464, 467, 17 L.Ed.2d 414 (1966)).

The railroads in this case as the Indian groups in Moe are beneficiaries of recently enacted nonexclusive grants of jurisdiction. Both groups reside near the center of the concern underlying the federal policy reflected in the laws enacted. The particular case which the railroad carriers press here bears more directly on the narrow situation contemplated by Congress than does the cause in Moe on the much broader grant of section 1362. See Moe, 425 U.S. at 473, 96 S.Ct. at 1641. The express words of exemption contained in the legislative history of section 11503 are a further recommendation not present in Moe against abstention. We conclude that the recent, specific expression of congressional intent and national policy reflected in section 11503 requires federal district courts to hear section 11503 cases brought before them. We find that the district court in abstaining abused its discretion, reverse and remand to district court for consideration on the merits.

VI. The Cross-Appeal.

The state board argues on cross-appeal that the injunction entered by the district court has prevented it from obtaining the undisputed portion of the railroads' tax bill. The state board also argues that the railroads will be unjustly enriched should the state not receive interest on the undisputed amount. We agree and order the district court to modify its injunction to allow the state to immediately assess and collect the undisputed amount of taxes without waiving its entitlement to the disputed amount. Furthermore the district court should require the railroads to pay interest on the undisputed amount of taxes and on any additional amount the court finds not in violation of section 11503 and the state chooses to assess and collect. The interest is to be assessed from the date such taxes would have become due but for the district court's injunction and at the rate set by Georgia law for taxes due but not paid from that date until payment is actually made.

REVERSED and REMANDED WITH INSTRUCTIONS.