The warning, which came Wednesday, said the plan may involve disrupting traffic on the Tampa Bay area's bridges during the convention, the Tampa Bay Times reported.
The FBI said it had intelligence indicating anarchists from New York "planned to travel to Tampa and attempt to close" all of the Tampa Bay-area bridges during the RNC.
"FBI and (Homeland Security) assess with high confidence anarchist extremists will target similar infrastructure in Tampa and Charlotte, with potentially significant impacts on public safety and transportation," the law enforcement alert states.
The Coast Guard said Thursday it will restrict boating within 50 yards of 15 Tampa Bay-area bridges during the convention. The ban on loitering, stopping, mooring or anchoring will be in place around the clock at the three main spans across Tampa Bay, the Times reported.
Closing the Tampa Bay-area bridges would be problematic, as many RNC attendees will be traveling to and from the Times Forum on charter buses every day of the convention, the newspaper said.
The Coast Guard also said it will impose security zones around cargo ships carrying anhydrous ammonia, liquified propane gas and ammonium nitrate near the Port of Tampa.