WASHINGTON (AP) — Federal prosecutors plan to seek a grand jury indictment of President Joe Biden's son Hunter before the end of the month, according to court documents filed Wednesday.

The filing came in a gun possession case in which Hunter Biden was accused of having a firearm while being a drug user, though prosecutors did not name exactly which charges they will seek. He has also been under investigation by federal prosecutors for his business dealings.

Prosecutors under U.S. Attorney for Delaware David Weiss, newly named a special counsel in the case, said they expect an indictment before Sept. 29.

Hunter Biden's lawyers, though, argued that prosecutors are barred from filing additional charges under an agreement the two sides previously reached in the gun case. It contains an immunity clause against federal prosecutions for some other potential crimes. Defense attorney Abbe Lowell said Hunter Biden has kept to the terms of the deal, including regular visits by the probation office.

"We expect a fair resolution of the sprawling, 5-year investigation into Mr. Biden that was based on the evidence and the law, not outside political pressure, and we'll do what is necessary on behalf of Mr. Biden to achieve that," he said in a statement.

Prosecutors have said that the gun agreement is dead along with the rest of the plea agreement that called for Hunter Biden to plead guilty to misdemeanor tax offenses. It fell apart after U.S. District Judge Maryellen Noreika raised questions about it during a court appearance in July.

The Justice Department did not have immediate comment.

News of a possible new indictment comes as House Republicans are preparing for a likely impeachment inquiry of President Biden over unsubstantiated claims that he played a role in his son's foreign business affairs during his time as vice president.

"If you look at all the information we have been able to gather so far, it is a natural step forward that you would have to go to an impeachment inquiry," House Speaker Kevin McCarthy, R-Calif., told Fox News recently.

The younger Biden has been the target of congressional investigations since Republicans gained control of the House in January, with lawmakers obtaining thousands of pages of financial records from various members of the Biden family through subpoenas to the Treasury Department and various financial institutions. Three powerful House committees are now pursuing several lines of inquiry related to the president and his son.

And while Republicans have sought to connect Hunter Biden's financial affairs directly to his father, they have failed to produce evidence that the president directly participated in his son's work, though he sometimes had dinner with Hunter Biden's clients or said hello to them on calls.

In recent months, Republicans have also shifted their focus to delving into the Justice Department's investigation of Hunter Biden after whistleblower testimony claimed he has received special treatment throughout the yearslong case.

Hunter Biden was charged in June with two misdemeanor crimes of failure to pay more than $100,000 in taxes from over $1.5 million in income in both 2017 and 2018. He had been expected to plead guilty in July, after he made an agreement with prosecutors, who were planning to recommend two years of probation. The case fell apart during the hearing after Noreika, who was appointed by President Donald Trump, raised multiple concerns about the specifics of the deal and her role in the proceedings.

If prosecutors file a new gun possession charge, it could run into court challenges. A federal appeals court in Louisiana ruled against the ban on gun possession by drug users last month, citing a 2022 gun ruling from the U.S. Supreme Court.

News of another indictment comes after U.S. Attorney General Merrick Garland named Weiss a special counsel, giving him broad authority to investigate and report out his findings and intensifying the investigation into the president's son ahead of the 2024 election.

The White House Counsel's office referred questions to Hunter Biden's personal attorneys.

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Associated Press writer Farnoush Amiri contributed to this report.