(CNN) Arizona Republican Senator Jeff Flake hit Donald Trump on trade Thursday, slamming the President for "acting on a whim to punish this country or that one," through trade tariffs.

"The Constitution gives Congress the primary role in regulating trade, and certainly tariffs, not the President," Flake told CNN's Brianna Keilar. "So, the President is using an exemption that was never intended for that purpose."

Flake joined Senate Foreign Relations Chair Bob Corker, a Tennessee Republican, and a bipartisan group of senators Wednesday sponsoring legislation that would require lawmakers to approve movement on trade from the White House on the basis of national security, stymieing the administration's tariffs on Canadian steel.

"This is the first time that a number of senators have actually stood up, a number of Senators from the President's party and said, 'No, you can't do that, and we're going to pass legislation to rein this in,'" Flake said. "And so that is our prerogative, that's what we should be doing, that's what we should have been doing sooner than now."

Corker's bill has faced significant pushback — CNN reported Trump called Corker Wednesday , encouraging the retiring senator to back off legislation in a "lengthy" call, while Republican Senate Majority Leader Mitch McConnell expressed his own antipathy , telling SiriusXM's Olivier Knox, "I don't think we need to be trying to rein in the President through legislation."

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