The watchdog group Media Matters, which has accused Fox News of spying on one of its employees, says the practice of targeting journalists goes back—way back, to the late 1990s.

“It also appears that Fox News Channel previously obtained telephone records of Media Matters founder David Brock in 1997,” the group’s attorney wrote on Friday to senior Fox executives and the attorney for Roger Ailes, the news channel’s founder and former chief. In a move that amounts to a prelude to potential litigation, the letters demanded that Fox “preserve all information” related to what Media Matters termed “surveillance” of its employees.

“As shown by earlier hacking scandals involving News Corp—affiliated entities, initial reports of these sorts of activities often reveal only the ‘tip of the iceberg,’” wrote the attorney, Marc Elias, who is also counsel for Hillary Clinton’s presidential campaign. “We expect to discover additional wrongdoing in the course of our investigation.”

The allegation is significant in that it tries to describe Fox News’ surreptitious gathering of phone records not as a one-time event, but as a pattern of behavior.

Media Matters president Bradley Beychok had previously told The Daily Beast that his group was aware of “allegations of email and phone records being obtained” of more than one Media Matters employee, but he didn’t specify Brock at the time.

The new reference to Brock appears to concern an allegation by a former Fox News executive, Dan Cooper, who spoke to Brock for a profile of Ailes in New York magazine in 1997. Cooper has said that he spoke to Brock on condition that he not be identified in the story. But before the story was published, Cooper says his agent got a threatening call from Ailes, who said he’d refuse to do business with any of the agent’s clients unless he dropped Cooper.

“I’ve thought to myself on many occasions, how did Roger find out prior to publication that Brock had interviewed me?” Cooper told The Daily Beast. Cooper concluded that Ailes may have obtained Brock’s phone records and saw that the two had been in communication with each other.

Cooper first made his allegations in 2008 in a lengthy post about his career as one of the architects of Fox News. That account grew into a self-published book that was critical of Ailes.

“Ailes knew I had given Brock the interview,” Cooper wrote. “Certainly Brock didn’t tell him. Of course. Fox News had gotten Brock’s telephone records from the phone company, and my phone number was on the list.”

Cooper’s charge resurfaced in 2011 amid the furor over phone hacking by Murdoch-owned journalistic outfits in Britain. While greeted skeptically by some at the time, his story appears to be gaining new traction as Media Matters considers whether to sue over the alleged targeting of its reporter, Joe Strupp. The allegations were first reported by Gabriel Sherman, a reporter for New York magazine and author of a book on Fox News and Ailes, The Loudest Voice in the Room.

Cooper told The Daily Beast that in order to rule out Brock having told Ailes himself that he spoke to the ex-Fox exec, he tried on numerous occasions to contact Brock and ask him. But, Cooper said, he never received a reply.

Finally, Cooper said, he persuaded a Media Matters employee to ask Brock.

“I want you to tell him, I have to have a denial, a definitive denial from David that he did not give up to Roger that I gave an interview,” Cooper said.

Cooper said the employee called back and said that she’d talked to Brock, and that he denied ever having told Ailes of their conversation.

According to Sherman, who cited two sources with direct knowledge of the incident, Fox’s general counsel, Dianne Brandi, “hired a private investigator in late 2010 to obtain the personal home- and cell-phone records” of Strupp. At the time, he had written articles quoting anonymous sources at Fox, “and the network wanted to determine who was talking to him,” Sherman reported.

Through a spokesperson, Brandi denied the allegations.

Legal experts told The Daily Beast that they knew of no way that a private investigator could legally obtain someone’s phone records without his consent. Sherman’s story made no claims on how the records were obtained.

In 2011, the FBI opened an investigation into News Corp. phone hacking and whether any illegal activity occurred in the United States. Specifically, investigators wanted to know if the phones of victims of the 9/11 attacks had been hacked.

Strupp confronted Murdoch that year about allegations of phone hacking in England and asked whether he could “assure Americans that there won’t be any phone hacking by the New York Post,” a News Corp. property, or by Fox News.

Murdoch repeatedly declined to answer Strupp’s questions, in an exchange that the reporter captured on video.