Democratic Representative Ilhan Omar is contesting the legality of a federal search of her Washington, DC-area home, with her attorneys demanding the return of property taken by agents and alleging that the investigation was politically motivated.

In a letter sent Friday to Justice Department prosecutors and obtained by CNN, Omar’s attorneys Amy Jeffress and Joshua Matz said the investigation violated the Minnesota congresswoman’s constitutional rights and threatened the separation of powers.

“This vindictive, retributive, and politically motivated criminal investigation into one of the President’s chief congressional critics violates Representative Omar’s constitutional rights and threatens the separation of powers,” the attorneys wrote.

Federal officers carried out the search early Monday after a federal magistrate judge approved a warrant, according to multiple people familiar with the investigation. The warrant reportedly imposed limits on the Justice Department’s access to Omar’s documents.

The investigation concerns alleged immigration fraud and is examining Omar, possible false statements on government documents and a potential conspiracy, according to the people familiar with the matter. Omar has been a frequent target of criticism from President Donald Trump’s administration.

Omar’s legal team rejected the premise of the inquiry, saying she fled Somalia in 1995 and became a lawfully naturalized US citizen in 2000. “There is no legitimate basis for any suggestion that she has violated any law concerning her citizenship status,” Jeffress and Matz wrote.

The lawyers said they had asked prosecutors to preserve all audio and video recordings made by federal agents during the search. Justice Department spokespeople did not immediately respond to CNN’s requests for comment on the allegations in the letter.

Questions over congressional protections

In their letter, Omar’s attorneys raised concerns about whether investigators followed procedures intended to protect the constitutional rights of members of Congress. They said the House of Representatives’ Office of General Counsel was not notified of the search until after it had been publicly reported.

According to the letter, the Washington judge had required particular notification procedures involving the House, Omar and her attorneys because of her constitutional protections as a lawmaker. Her defense team said investigators may have violated her rights by failing to comply with those conditions.

The attorneys also said no representative from the US attorney’s office or the Justice Department was present to explain Omar’s protections under the Speech or Debate Clause. Instead, they said, she was given a waiver that she did not sign. The letter further alleged that Omar’s lawyers were not given an opportunity to identify or separate materials protected by the clause.

Jeffress and Matz described the search as stemming from a “years-old, tired conspiracy theory.” They noted that it occurred less than three weeks before Election Day and argued that the department has historically avoided comparable investigative activity so near an election to prevent even an appearance of political motivation.

“But the political motivations behind this pre-election investigation and search are clear as day,” the attorneys wrote in the letter, which was first reported by The Wall Street Journal. “For the reasons given above, this search was neither justified nor lawful.”

The lawyers also said search-warrant documents repeatedly referred to the congresswoman by her first name. They asked federal agents to use Omar’s proper title in future dealings.