Ala. Code § 40-23-65
If a sales or use tax equal to or greater than the amount of the Alabama tax is paid to another state under a requirement of law, the property which is the subject of such tax when imported for use or consumption in Alabama is not subject to the use tax, which is required to be paid by Section 40-23-61. If the amount of tax paid to the other state is less than the Alabama tax, then the difference between the out-of-state tax and the Alabama tax must be paid. No credit will be allowed for taxes paid on tangible personal property in any state which does not give credit for taxes paid on similar property in Alabama. The Commissioner of Revenue shall require such proof of payment of tax to another state as he deems to be necessary and proper.
The Commissioner of Revenue shall adopt such rules and regulations as he deems necessary for the proper administration of this section.
Ala. Code § 40-23-65 (1975)