Sen. Jeff Flake (R-Ariz.) warned Sunday that he’s prepared to oppose President Donald Trump’s judicial nominees unless the Senate votes on legislation curtailing the president’s power to unilaterally impose tariffs on other countries.

“I think myself and a number of senators, at least a few of us, will stand up and say, ‘Let’s not move any more judges until we get a vote, for example, on tariffs,’” Flake, who is retiring this year, said on ABC’s “This Week.”

Flake serves on the Judiciary Committee, where Republicans maintain a narrow one-seat majority. If he joins Democrats on the committee in not allowing Trump’s judicial nominees a floor vote, he’d have substantial leverage over Senate Majority Leader Mitch McConnell (R-Ky.), who has made confirming judges a top priority.

“On something like tariffs, for example, the Senate ought to bring legislation to the floor that says, ‘Hey, we’re going push back here.’... Canada, Mexico are not national security threats,” Flake added on ABC. “The European Union exporting cars to the U.S. does not represent a national security threat, and we ought to push back. And if we don’t, why are we there?”

Trump’s tariffs on allies in the European Union, Canada and Mexico have generated sharp criticism from some Republicans, who warn they will hamstring the nation’s humming economy and cost Americans jobs. Trump on Friday further threatened to escalate a trade war with Europe by imposing a 20 percent tariff on all U.S. imports of European Union-assembled cars.

GOP leaders in Congress, however, have so far resisted directly challenging Trump on trade, worrying that a messy intraparty clash would prove to be damaging ahead of the crucial November midterm elections.

Sen. Bob Corker (R-Tenn.) has introduced a bill with Sen. Pat Toomey (R-Pa.) aiming to limit the president’s authority under Section 232 of the Trade Expansion Act of 1962 to levy tariffs based on “national security grounds” ― a provision Trump has invoked several times. They argue he has abused the law, and that Congress should get a say in the matter.

In a separate interview on Sunday, Corker said Trump may face a “jailbreak” in Congress over tariffs ― suggesting that he too was willing to force the issue.

“There’s not a person at the White House that can articulate why they are doing this,” Corker said on CBS’ “Face the Nation.”

Flake has already held up the nomination of Britt Grant, a Trump nominee from Georgia for the U.S. Court of Appeals for the 11th Circuit. He declined to tell reporters why last week, however, stating that “it’s just something I’m working out.”

In addition to using judicial appointments as leverage on tariffs, Flake is also willing to oppose Trump nominees in order to “spur discussions on travel restrictions to Cuba,” according to CNN.

“Unless we can actually exercise something other than just approving the president’s executive calendar, his nominees, judges ... we have no reason to be there,” Flake said of Senate Republicans.

Flake often speaks out against Trump’s inflammatory rhetoric and controversial policies. Earlier this year, he delivered an impassioned speech from the Senate floor denouncing Trump for disregard for the truth and his GOP colleagues’ unwillingness to stand up to him.