Okla. Stat. tit. 62 § 304.2
Except as otherwise provided by Section 165.3a of Title 40 of the Oklahoma Statutes, assignment of salary or wage earnings in such instance shall be by separate instrument, and by affidavit. Except as otherwise provided by Section 165.3a of Title 40 of the Oklahoma Statutes, it shall be unlawful to issue or authorize the issuance of a municipal warrant for salary or wages to any person other than the person earning the same, or to his or her assignee or the executor or administrator of his or her estate or to any person entitled to child support payments pursuant to an income assignment proceeding or a garnishment proceeding. Except as provided by income assignment procedures for the collection of child support, no assignment of a part of salary or wages shall be made, and any assignment of salary or wages before the same has been earned shall be a nullity and shall avail the assignee nothing.
Okla. Stat. tit. 62, § 304.2