Treasury Secretary Steve Mnuchin wants the courts to decide whether he is allowed to defy a congressional request for the President’s tax returns.

During a Wednesday Senate appropriations subcommittee hearing, Sen. Chris Van Hollen (D-MD) asked whether he believes that Congress has a “legitimate interest” in reviewing Trump’s returns.

“There is a difference in interpretation between Congress and us and the Department of Justice around this law,” Mnuchin said during his testimony before Senate Appropriations.

He went on to offer a civics lesson to the senator: “This is why there are three branches of government. If there is a difference of opinion, this will go to the third branch of government.”

Rep. Richard Neal (D-MA) issued a subpoena for Trump’s returns on Friday, after sending a request for them in April under a 1924 statute that empowers the chairman of the House Ways and Means committee to demand the returns of any filer. The statute states that the Treasury Secretary “shall furnish” the returns to Congress.

Mnuchin has refused the requests so far. His appearance before the Senate on Wednesday marks his first public comments on the matter since receiving the subpoena.

Mnuchin’s testimony before Congress suggests what has long been suspected: that the request will end up in a lengthy court battle.

Neal did not send the request to Mnuchin, but rather to IRS Commissioner Chuck Rettig. Nevertheless, Mnuchin has taken the lead in correspondence with Congress over the matter.

In later questioning from Sen. Chris Coons (D-DE), Mnuchin said that Rettig “concurred” with his decision.

“He has specifically sent notices to Ways and Means concurring with my decision,” Mnuchin said.