LOS ANGELES -- U.S. President Donald Trump asked a federal judge on Monday to order private arbitration in a case brought by a porn actress who claimed she had an affair with him.

Trump and his personal attorney, Michael Cohen, filed papers in federal court in Los Angeles asking a judge to rule that Stormy Daniels' case involving a non-disclosure agreement must be heard by an arbitrator instead of a jury.

Daniels, whose real name is Stephanie Clifford, has been seeking to invalidate the agreement she signed days before the 2016 presidential election. She has offered to return the $130,000 she was paid as she tries to "set the record straight."

She's said she had sex with Trump once in 2006 and their relationship continued for about a year. Trump married his current wife, Melania Trump, in 2005, and their son, Barron, was born in 2006.

The White House has said Trump denies having an affair.

Trump's attorneys have argued that Daniels could owe about $20 million for violating the non-disclosure deal.

Daniels argues the agreement is legally invalid because it was only signed by her and Cohen, not by Trump.

In the Monday court filing, Cohen said Daniels had never raised any issues with the settlement agreement or suggested it was invalid or legally unenforceable before she filed her lawsuit last month.

Daniels' attorney, Michael Avenatti, said they would oppose the motion to have the case heard in private arbitration, "hidden from the American public."

"This is a democracy and this matter should be decided in an open court of law owned by the people. #sunlight," he tweeted.