Former Supreme Court Justice John Paul Stevens said he is concerned President Trump is crossing a line in refusing to comply with House subpoenas.

“I think there are things we should be concerned about, there’s no doubt about that,” the 99-year-old told the Wall Street Journal.

“The president is exercising powers that do not really belong to him. I mean, he has to comply with subpoenas and things like that,” he said.

The standoff between the Trump administration and the Democratic-controlled House has escalated in recent weeks after the White House ordered former White House counsel Don McGahn and the former personnel security director to not comply with subpoenas.

The House Judiciary Committee voted Wednesday to hold Attorney General William Barr in contempt of Congress after Trump asserted executive privilege over special counsel Robert Mueller’s report and the underlying evidence.

If the dispute ends up at the Supreme Court, Stevens said it’s obvious the justices should rule in favor of the House.

“I wouldn’t want to predict that anybody’s going to take the incorrect view,” he said. “But certainly, the correct view is pretty clear.”

Stevens, who retired in 2010, was nominated by Republican President Gerald Ford and went on to be part of the court’s liberal bloc.