AT&T made a “serious misjudgment” to seek advice from President Trump’s personal attorney, Michael Cohen, AT&T chief executive Randall Stephenson told employees in a companywide internal email Friday.

“There is no other way to say it — AT&T hiring Michael Cohen as a political consultant was a big mistake,” Stephenson wrote.

Bob Quinn, a top AT&T executive in the company’s Washington offices, will be retiring, Stephenson said.

The email comes after revelations that AT&T agreed to pay $600,000 to Cohen last year in exchange for advice on how to approach the Trump administration. Internal AT&T documents, obtained by The Washington Post on Thursday, outlined how Cohen was expected to provide guidance on matters facing the company at the Federal Communications Commission and the Justice Department, specifically mentioning AT&T’s $85 billion Time Warner merger.

AT&T’s ties to Cohen have prompted questions from U.S. lawmakers about whether AT&T sought to influence the government’s independent merger review.

“Everything we did was done according to the law and entirely legitimate,” Stephenson wrote. Companies routinely hire political consultants at the outset of new administrations, he said, and AT&T has done so in the past.

But, Stephenson added, AT&T’s Washington team failed to fully vet Cohen before hiring him, and that Stephenson takes responsibility.

In a supplemental document linked from the email, Stephenson explained that Cohen was the one who approached the company offering insight on the administration’s “key players, their priorities and how they think.”