Horizon Lines Inc. said it has placed six employees involved in the Puerto Rico trade lane on administrative leave as a result of management's review of issues raised by the Department of Justice investigation of pricing practices of some domestic shipping companies.

Two of the six employees subsequently submitted their resignation, according to a news release from Horizon, the second-largest shipping company serving Hawai'i. Horizon, based in Charlotte, N.C., "continues to fully cooperate with the Department of Justice in its investigation," according to the release.

Federal agents armed with search warrants and a grand jury subpoena last month searched Horizon's Charlotte offices and removed computers and boxes.