The U.S. Justice Department is investigating whether Fox News failed to inform shareholders about settlements made with employees who charged former chairman and CEO Roger Ailes with sexual harassment, a source with knowledge of the matter told CNNMoney.

The investigation, which has been going on for months, came to light on Wednesday after attorney Judd Burstein, who represents clients who have brought sexual harassment charges against Ailes, announced in a court hearing that one of his clients had received a subpoena relating to "alleged violations of criminal law by Fox."

"I was told by the U.S. attorney's office there is an ongoing criminal investigation, relating to these allegations, all of these allegations," Burstein said, according to The New York Daily News. The subpoena, which was issued by U.S. Attorney Preet Bharara's office, included "alleged violations of criminal law by Fox," Burstein said.

On Wednesday afternoon, a Fox News spokesperson acknowledged that Fox News had been in communication with the U.S. Attorney's office but did not specify if the network was the subject of the investigation.

"Neither FOX News nor 21CF has received a subpoena, but we have been in communication with the U.S. Attorney's office for months — we have and will continue to cooperate on all inquiries with any interested authorities," the spokesperson said.

On Wednesday night, however, a source with knowledge of the matter confirmed that Fox News was the subject of the investigation. The settlements in question date back several years, the source said.

Burstein's remarks were first reported by The New York Daily News and The Hollywood Reporter. He did not respond to requests for further comment.

Burstein was in court representing former Fox News host Andrea Tantaros on sexual harassment claims she has made against Ailes and Fox News. Burstein did not identify which one of his clients received the subpoena, but said he believed Tantaros would receive one as well.

In a court motion filed last August seeking to compel arbitration of Tantaros' claim, Fox News alleged that she "is not a victim; she is an opportunist."

Responding to Burstein's comments on Wednesday, the Fox News spokesperson noted that Tantaros' case had been moved to arbitration, and accused Burstein of "histrionics."

"The court granted Fox News' motion to send Andrea Tantaros' case to arbitration, where it always belonged, and rejected her counsel Judd Burstein's histrionics," the spokesperson said.

Fox News has settled sexual harassment complaints by several women, including a reported $20 million settlement with former Fox anchorwoman Gretchen Carlson.