Hunter Biden will ask a judge to throw out his federal indictment on felony gun charges, his attorneys said in a court filing late Thursday.

His attorneys said they will ask for the case to be dismissed because, in their view, special counsel David Weiss was prohibited by a previous agreement from bringing the indictment.

"Mr. Biden maintains that the 'stand alone,' 'bilateral' Diversion Agreement that both parties signed remains in force, and he will seek to dismiss the Indictment against him pursuant to the immunity provisions of that Agreement," Biden's attorney Abbe Lowell wrote in the filing.

Weiss said in a Wednesday filing that the "proposed diversion agreement" wasn't signed by a court official as required, and therefore, "it did not enter into effect." The two sides have been fighting for the past two months over whether the deal to resolve the gun offense is still valid and legally binding.

Hunter Biden pleaded not guilty on Tuesday to three federal crimes related to his purchase of a revolver at a Delaware gun shop in 2018. It was the first-ever prosecution by the Justice Department of the child of a sitting president.

Federal prosecutors say Biden broke the law by lying on a Bureau of Alcohol, Tobacco, Firearms and Explosives form when he swore that he was not using, and was not addicted to, any illegal drugs -- even though he was struggling with crack cocaine addiction at the time. It's a federal crime to lie on that form or to possess a firearm as a drug user. Biden owned the gun for about 11 days in 2018.

As part of the so-called "diversion agreement," Weiss' team provisionally filed one gun charge against Biden but promised to dismiss the charge in two years if he passed drug tests and stayed out of legal trouble. But that agreement, and a related plea deal involving tax misdemeanors, collapsed over the summer, leading to the gun indictment. Weiss has said he's still mulling an indictment on tax charges.