Ala. Code § 40-23-106
If a sales or use tax equal to or in excess of the amount of the tax imposed by this article is paid to another state under a requirement of the law of that state, the automotive vehicle, motorboat, truck trailer, semitrailer, or house trailer which is the subject of the tax when it is imported for use, storage, or consumption in this state shall not be subject to the use tax imposed by this article. If the amount of the tax paid to another state is less than that imposed by this article, then the difference shall be paid. However, no credit shall be allowed for taxes paid on any automotive vehicles, motorboats, truck trailers, semitrailers, or house trailers in any other state which does not extend credit for taxes paid on similar property in Alabama. The licensing official shall require proof of payment of tax in another state deemed necessary and proper.
Ala. Code § 40-23-106 (1975)