An American judge has threatened to ban Carnival Corporation ships from using US ports after receiving evidence the line had tried to evade ship pollution audits.

United States Federal District Judge Patricia Seitz also threatened to send the  “members of Carnival’s executive committee” to a “detention centre for a couple of days” for violation of the terms of its probation for pollution offences.

Quite how either of these punishments could be carried out remains unclear. Carnival is one of the world’s biggest lines, and owns 10 brands and operates 102 ships.

In a statement, Carnival Corp.’s chief communications officer Roger Frizzell told The Miami Herald: “It appears there were some mischaracterisations made by others to the court. We intend to fully address the issues raised at today’s court conference.

“Our environmental responsibility has been and continues to be a top priority for the company. Our aspiration is to leave the places we touch even better than when we first arrived.”

Judge Seitz said she would make a decision on the evidence in June, and demanded the chairman and president appear before her.

“The people at the top are treating this as a gnat,” Seitz said.

She added she received a 45-minute presentation as a guest aboard Carnival Corp.’s ultra-luxury cruise line Seabourn about how damaging plastic straws are to the marine environment.

“I was thinking to myself, ‘I’m impressed,’ ” she reportedly said. “Obviously they talk the talk, but they’re not walking the walk.”

Carnival has served two of a five year probation term  as part of a $40 million settlement for illegally dumping oil into the ocean from its Princess Cruises ships over a period of some eight years.

According to court filings reported by American news outlets, Carnival Corporation and its subsidiary cruise lines allegedly sought to “prepare ships in advance of court-ordered audits, falsified records, dumped plastic garbage into the ocean and illegally discharged grey water into Glacier Bay National Park in Alaska”.

The company’s “probation” began in April 2017, and as a condition it was required to cooperate with a third party auditor to inspect its ships.

But according to court files, the company had a program in place to prepare for court-ordered audits to avoid any negative findings by the independent court-appointed monitor.

Seitz ordered Carnival to stop the practice in December 2017, and the company said it had done so. But federal prosecutors allege that Carnival continued the practice into 2018.

The Miami Herald reported Prosecutors cited internal emails shared at Carnival’s brands discussing how to prepare for the audits.

“It would be really important to go onboard on August 12 for one week in order to have time to manage issues before the audits and avoid findings,” said a 2017 internal email from Carnival’s German-based cruise line AIDA Cruises.

A similar internal email from Carnival’s Seattle-based Holland America Line mentioned “prevent audit findings” as a goal in early 2018.

According to court filings, the court-appointed monitor found that Carnival and its subsidiaries have repeatedly falsified records while on probation as recently as September 2018, when a second engineer on Holland America’s Westerdam ship falsified maintenance records to make it look like he had cleaned and tested equipment when he had not.