Amends the Internal Revenue Code to apply the harbor maintenance tax to certain ports used to import commercial cargo worth more than $100,000,000. Negates the tax on a port for any year after a period of three consecutive years in which $100,000,000 or less cargo was imported through the port and no Federal funds were used for construction, maintenance, or operation, as well as for subsequent years so long as the preceding year's cargo was $100,000,000 or less.