Puerto Rico Economic Activity Credit Improvement Act of 1999

Puerto Rico Economic Activity Credit Improvement Act of 1999 - Amends the Internal Revenue Code to modify the requirements for corporations to be eligible for the Puerto Rico economic activity credit. Requires that, in determining the credit amount, the credit provisions be applied separately to each substantial line of business of the corporation. Removes provisions limiting, in taxable years beginning after 2001, the aggregate taxable income taken into account in determining the amount of the credit.

Amends provisions relating to the Puerto Rico and possession tax credit to modify, with respect to possessions other than Puerto Rico, corporate eligibility requirements. Requires that, in determining the credit amount, the credit provisions be applied separately to each substantial line of business of the corporation. Modifies additional restricted credit requirements. Sets forth credit rules applicable to Guam, American Samoa, and the Commonwealth of the Northern Mariana Islands.