Carnival Corp., the world’s largest cruise operator, said the U.S. Justice Department joined a U.K. investigation into whether its Caribbean Princess ship violated international pollution laws.

Carnival is cooperating with the probe and is also conducting an inquiry of its own, according to a filing today. The U.K. Maritime & Coastguard Agency had initiated an investigation on Aug. 28, the Miami-based company said in a separate filing last year.

Carnival reached an agreement in September with the U.S. Environmental Protection Agency to spend $180 million to cut sulfur emissions from 32 ships after pressure to clean up pollution the cruise operator causes near ports.

Under that pact, the company was to install scrubbers and diesel particulate filters on its ships to cut pollutants that can exacerbate smog or reduce microscopic particles dangerous to humans’ lungs.

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Separately, Carnival said its Costa division terminated a general sales agent agreement with Boutimar Travel Co., after discovering the company’s Iranian origin and concluding the accord violated the cruise operator’s compliance policy.

None of the guests who purchased cruises through Boutimar were on the Specially Designated Nationals and Blocked Persons List maintained by the U.S. Office of Foreign Assets Control, according to today’s filing. The aggregate cruise ticket payments received by Costa from those guests were approximately $215,000, net of $31,000 of retained commissions,