Acting Attorney General Matt Whitaker is set to stiff-arm Congress.

Unless House Judiciary Committee Chairman Jerry Nadler promises—in writing —not to subpoena him today or tomorrow during his testimony, Whitaker will not testify, according to a letter the Justice Department sent to Nadler Thursday afternoon.

The Justice Department’s head of legislative affairs, Stephen Boyd, wrote in the letter that unless Nadler’s committee promises by 6 p.m. Thursday not to subpoena Whitaker, he will not show up.

The committee voted on Thursday morning to let Nadler subpoena Whitaker if he so chooses. Boyd fired back in his letter, calling the move an effort “to transform the hearing into a public spectacle.”

According to the letter, Whitaker intends to refuse to answer some of the committee’s biggest questions, invoking executive privilege.

“It is clear that your proposed questions seek the kind of information that the Executive Branch has, during Administrations of both parties, historically declined to provide to the Congress,” Boyd wrote.

The letter also says Whitaker would testify that he did not promise Trump anything regarding the Mueller probe before becoming acting attorney general.

“The Acting Attorney General will testify that at no time did the White House ask for, or did the Acting Attorney General provide, any promises or commitments concerning the Special Counsel’s investigation,” the letter said.

“[T]he Acting Attorney General will make clear that there has been no change in how the Department has worked with the Special Counsel’s office,” the letter added.

Boyd’s letter responded to a list of questions Nadler sent to Whitaker on Jan. 22 of this year. In that letter, Nadler made clear that he wants Whitaker to answer questions about the acting attorney general’s conversations with President Donald Trump.

Those questions include: Did Whitaker talk with Trump about taking over the Justice Department’s top job before the president fired then-Attorney General Jeff Sessions? Did he tell the president anything he learned from Special Counsel Robert Mueller about the Russia probe? And did the president “lash out” at him over the Southern District of New York’s court filings about Michael Cohen?

If the hearing still happens, it will be the first blockbuster showdown between newly empowered Hill Democrats and a top Trump administration official. Justice Department officials have been preparing for the hearing for weeks, bracing for scorching questions.