CHARLOTTE, N.C. -- Horizon Lines Inc. said it will "vigorously defend" itself against a securities class-action lawsuit related to alleged price-fixing at its Puerto Rican shipping operations.

The Charlotte-based ocean shipping company said the lawsuit, brought by individuals that have owned its stock between March 2, 2007 and April 25, 2008, claims it made "material misstatements and omissions" about the business' pricing practices.

The lawsuit was filed in the U.S. District Court for the District of Delaware. The company acknowledged the lawsuit in a statement late Friday.

Federal agents raided Horizon's Charlotte headquarters in April as part of an investigation of pricing practices of ocean carriers operating in Puerto Rico. An antitrust lawsuit filed in Puerto Rico's U.S. District Court earlier that month alleged that Horizon and three other shippers conspired to inflate prices for transporting goods to the island and added illegal surcharges.

A month later Horizon Lines suspended six employees amid an ongoing Department of Justice investigation into ocean shipping prices. The workers, who were involved in the Puerto Rico trade lane, were placed on administrative leave following a review by the company into issues raised by federal investigators. Two of the employees later submitted their resignations.

Horizon Lines owns or leases a fleet of 21 U.S.-flag containerships and five port terminals linking the continental United States with Alaska, Hawaii, Guam, Micronesia and Puerto Rico. It also offers logistics services to shippers.