A conservative lawyer who aided former President Donald Trump's efforts to undo the 2020 election results and who has been repeatedly referenced in House hearings on the Jan. 6, 2021 assault on the Capitol said in a court filing Monday that federal agents seized his cellphone last week.

John Eastman said the agents took his phone as he left a restaurant last Wednesday evening, the same day law enforcement officials conducted similar activity around the country as part of broadening probes into efforts by Trump allies to overturn the election.

The move underscores federal investigators' interest in the unsuccessful schemes advanced by Trump advisers to help keep the Republican president in power in the period between the November 2020 election and the riot at the Capitol two months later, when Trump loyalists stormed the building to halt the certification of the election results.

Eastman said the agents who approached him identified themselves as from the FBI but appeared to be serving a warrant on behalf of the Justice Department's Office of Inspector General, which he contends has no jurisdiction to investigate him since he has never worked for the department. He said the cellphone that was seized contains emails that have been the subject of a months-long dispute between him and the House panel.

"That litigation has received extensive media attention, so it is hard to imagine that the Department of Justice, which apparently submitted the application for the warrant at issue here, was not aware of it," wrote his lawyers, Charles Burnham and Joseph Gribble.

The action was disclosed in a filing in federal court in New Mexico in which Eastman challenges the legitimacy of the warrant, calling it overly broad, and asks that a court force the federal government to return his phone. He says the warrant does not specify any particular crime for which evidence from the phone might be relevant.

The filing does not specify where exactly agents seized his phone, though the warrant was signed by a federal magistrate judge in New Mexico and footage of the seizure aired by Fox News on Monday night describes it as having occurred in the city of Santa Fe. Lawyers for Eastman did not immediately return an email seeking comment.

Federal agents investigating the run-up to the Jan. 6 riot last week served a raft of subpoenas related to a scheme by Trump allies to put forward alternate, or fake, slates of electors in hopes of invalidating the election won by Democrat Joe Biden. Also that day, agents searched the Virginia home of Jeffrey Clark, a Trump Justice Department official who encouraged Trump's challenges of the election results.

A spokeswoman for the inspector general's office declined to comment.

Eastman, who last year resigned his position as a law professor at Chapman University, has been a central figure in the ongoing hearings by the House committee investigating the riot at the Capitol, though he has not been among the witnesses to testify.

The committee has heard testimony about how Eastman put forward a last-ditch, unorthodox proposal challenging the workings of the 130-year-old Electoral Count Act, which governs the process for tallying the election results in Congress.

Eastman pushed for Vice President Mike Pence to deviate from his ceremonial role and halt the certification of the electoral votes, a step Pence had no legal power to take and refused to attempt. His plan was to have the states send alternative slates of electors from states Trump was disputing, including Arizona, Georgia, Michigan, Pennsylvania and Wisconsin.

With competing slates for Trump or Biden, Pence would be forced to reject them, returning them to the states to sort it out, under the plan.

A lawyer for Pence, Greg Jacob, detailed for the committee at a hearing earlier this month how he had fended off Eastman's pressure, and another witness, retired federal judge Michael Luttig, has called the plan from Eastman "incorrect at every turn."

The panel played video showing Eastman repeatedly invoking his Fifth Amendment right against self-incrimination while being interviewed by the committee.

Eastman later sought to be "on the pardon list," according to an email he sent to Trump lawyer Rudy Giuliani, shared by the committee.