The Department of Justice has opened a criminal investigation into Federal Reserve Governor Lisa Cook, sources familiar with the matter said Thursday.

Bill Pulte, the Director of the Federal Housing Finance Agency, sent the Department of Justice two criminal referral letters about Cook last month regarding Cook’s properties in Georgia and Michigan.

Federal investigators have begun issuing subpoenas and are utilizing grand juries in both states as part of their investigation, the sources said.

The Wall Street Journal first reported the existence of the criminal investigation.

As President Donald Trump seeks to reshape the balance of the Federal Reserve central banking system, Pulte’s allegations have become the basis of Trump’s effort to terminate Cook “for cause” — a controversial and legally fraught move that is actively being challenged in court.

In an Aug. 15 letter to Attorney General Pam Bondi and Special Attorney for Mortgage Fraud Ed Martin, Pulte alleged that Cook “falsified bank documents and property records to acquire more favorable loan terms, potentially committing mortgage fraud under the criminal statute.” Pulte has claimed that the referral was based on publicly available information but has declined to comment about the tip that prompted his investigation. The first referral focused on Cook’s properties in Georgia and Michigan.

Reached for comment regarding the DOJ probe, attorneys for Cook said in a statement, “Predictably and recognizing the flaws in challenging their illegal firing of Governor Cook, the administration is scrambling to invent new justifications for its overreach.”

“This Justice Department — perhaps the most politicized in American history — will do whatever President Trump demands. He wants cover, and they are providing it,” said attorney Abbe Lowell. “The questions over how Governor Cook described her properties from time to time, which we have started to address in the pending case and will continue to do so, are not fraud, but it takes nothing for this DOJ to undertake a new politicized investigation, and they appear to have just done it again.”

Following the Aug. 15 referral, Martin sent a letter to Federal Reserve Chairman Jermone Powell encouraging him to fire Cook because of the ongoing investigation.

“At this time, I encourage you to remove Ms. Cook from your Board. Do it today before it is too late! After all, no American thinks it is appropriate that she serve during this time with a cloud hanging over her,” Martin wrote.

Days later, Trump attempted to fire Cook based on the allegations that she designated both her homes in Georgia and Michigan as her primary residence. Cook has denied wrongdoing, said she would continue to serve in her role, and sued to challenge Trump’s attempt to remove her.

“President Trump has no authority to remove Federal Reserve Governor Lisa Cook. His attempt to fire her, based solely on a referral letter, lacks any factual or legal basis. We will be filing a lawsuit challenging this illegal action,” said Lowell.

Later that month, on Aug. 28, Pulte sent a second referral letter to the Department of Justice, alleging that Cook had made “multiple false representations” while serving as a Federal Reserve governor, including listing an apartment in Massachusetts as both an investment property and a second home.

In the following days, Pulte has made multiple comments on social media accusing Cook of crimes and calling for her prosecution, unusual steps during an ongoing investigation before any formal determinations of wrongdoing.

“The damage currently being done to the integrity of the Federal Reserve, by Lisa Cook and Jerome Powell, cannot be overstated,” he wrote in one post.

On Thursday, Pulte originally planned to hold a press conference in front of the Elijah Barrett Prettyman U.S. Courthouse in Washington, D.C. where he said he would share new information about Cook.

He later canceled the press conference, writing on social media, “Out of respect for the process, I will be delaying this press conference.”