Business Activity Tax Simplification Act of 2003 - Amends Federal law concerning the taxation of interstate commerce to expand the scope of the protections prohibiting taxation by jurisdictions of the income of out-of-state corporations whose in-state presence is nominal from just tangible personal property to include intangible property and services.
Requires an out-of-state company to have a physical presence in a State before the State can impose franchise taxes, business license taxes, and other business activity taxes.