Tax Law, § 504, subd. 4
A motor vehicle having a maximum gross weight of 18,000 pounds or less is exempt unless the carrier elects the unloaded weight method of computing the tax (see § 481.1et seq.). If such election is made, a permit and plate must be obtained for every tractor having an unloaded weight in excess of 4,000 pounds and every truck having an unloaded weight in excess of 8,000 pounds, even if the maximum gross weight is 18,000 pounds or less.
N.Y. Comp. Codes R. & Regs. Tit. 20 § 471.6