Rep. Jason Chaffetz (R-UT), the chair of the House Oversight Committee, sent a letter to the director of the Office of Government Ethics on Thursday demanding that he sit for an interview with the committee about his public statements on Donald Trump.

Chaffetz’s letter follows public remarks from the office’s director, Walter Shaub Jr., during which he criticized Trump’s plans to separate himself from his business as inadequate. But the letter did not mention that speech. Chaffetz focused on a series of tweets published by the Office of Government Ethics in November praising Trump for divesting, even though the President-elect had not made any such announcement, and encouraging Trump to make a clean cut from his business when he takes office. The tweets also revealed that the ethics office had discussed divestiture with the Trump transition team.

In his letter, Chaffetz said he was concerned that the Office of Government Ethics was “blurring the line between public relations and official ethics guidance.” He said that the tweets about Trump’s plans to address potential conflicts of interest were confusing since they made it unclear whether the office approved of Trump’s plans.

The oversight chair also mentioned comments the office made in 2015 about paid speeches given by Hillary Clinton, criticizing the office for commenting on a situation that the office had not fully investigated.

Chaffetz noted in the letter that the Oversight Committee has the authority to shut the ethics office down and asked Shaub to sit for an interview by the end of January.

In a Thursday interview with Politico, Chaffetz criticized Shaub’s public statements.

“He seems to be acting prematurely at best, without doing investigations or thorough looks,” Chaffetz said. “He’s rendering opinions publicly that really cause you to scratch your head. We need the Office of Government Ethics to act ethically. Ironically, that’s not what they’re doing.”

Chaffetz told Politico that Shaub has not agreed to a meeting requested by the Oversight Committee since the election and threatened to subpoena Shaub.

“He is coming in. This is not going to be an optional exercise,” Chaffetz said.

“We need a fair person behind the plate that’s going to call balls and strikes,” he added. “What they’re supposed to do is help work with somebody to comply with the ethics requirements. But when you talk publicly about private conversations, that’s not ethical. And when you refuse to come in and talk to the committee when you’re doing reauthorization, when you start tweeting and issuing press statements on things you never looked at, that shouldn’t be the case at all.”