Ala. Code § 40-18-23
Any taxpayer who has taxable income from business activities both within and without this state, whose only business activities within this state consist of sales and do not include owning or renting real estate or tangible personal property, and whose dollar volume of gross sales made during the tax year within this state is not in excess of $100,000 may elect to report and pay any income tax due on the basis of a percentage of such volume. If a taxpayer elects to report and pay income tax due on the basis of a percentage of sales in this state, the percentage rate shall be one fourth of one percent of such volume of sales. The report shall be made on forms prescribed by the Commissioner of Revenue and shall be due and payable on the same date and in the same manner as provided in Sections 40-18-27 and 40-18-39.
Ala. Code § 40-18-23 (1975)