SAN JUAN, Puerto Rico — Shipping companies allegedly conspired to inflate prices for transporting goods to Puerto Rico and added illegal surcharges, according to an antitrust lawsuit filed in the island's U.S. District Court.

The suit seeks unspecified damages from several U.S. companies, including one headquartered in North Carolina, and it comes amid an FBI investigation into pricing practices of ocean carriers operating in the territory.

The suit was filed Tuesday by a law firm representing La Esperanza Bus Line, which ships buses to Puerto Rico from the U.S. mainland.

It alleges that Horizon Lines Inc., Sea Star Line LLC, Crowley Maritime Corp. and Trailer Bridge Inc. colluded in violation of antitrust laws, resulting in higher prices for goods sold across the island, said San Juan-based attorney Eric Quetglas.

Last month, agents searched the Puerto Rico offices of Horizon and Sea Star, as well as Horizon's headquarters in Charlotte, N.C. Horizon spokeswoman Barbara Yeninas declined to comment, but the company said at the time that it was cooperating with officials and that the probe involves the U.S. Justice Department's antitrust division.

Phone messages left with the other companies were not immediately returned.

Justice spokeswoman Gina Talamona said last week that the antitrust division is investigating allegations of anticompetitive pricing in the coastal freight shipping industry. She did not give further details.