Donald Trump’s threats to exit the North American Free Trade Agreement may well be within the bounds of a president’s power. But legal experts warn such a move could be tested by heavy congressional fire and lengthy court battles.

There’s no legal consensus whether the U.S. president can act on his own to end the tariff-free benefits of Nafta without lawmakers’ approval. Trump seems to think he can, and warned as recently as Monday that he may terminate the trade accord he has assailed as a bad deal for American workers.

The process would require giving Mexico and Canada six-months notice of America’s intent to withdraw, during which time Trump’s administration could continue trying to negotiate a better deal. But the exit clause is an untested provision of Nafta, so it’s unclear exactly what would happen after the clock runs down if there’s still no new deal.

Trump’s strategy could be to put pressure on Mexico and Canada—with an ultimatum of agreeing to his demands or else. So far those trading partners are calling his threats scare tactics ahead of the second round of negotiations from Sept. 1-5 in Mexico City.

Here are a few of those expert opinions on Trump’s power to act without Congress:

“If I were advising him, I’d say, ‘Look, even if you think you have the power to get rid of the whole thing, you should go to Congress because there’s no certainty you’ll be able to get rid of the whole thing”’: Hofstra University Law Professor Julian Ku.
“The president generally has the ability to withdraw the United States from international agreements—that’s part of his constitutional executive power in foreign affairs”: University of San Diego School of Law Professor Michael Ramsey.
“Despite the president’s ability to withdraw from the agreement, the repeal of statutory provisions implementing Nafta would likely require congressional assent”: Congressional Research Service in May 2017 report.
“There’s no statutory delegation to terminate U.S. participation in these treaties”: Joel P. Trachtman, professor of international law at Tufts University’s Fletcher School of Law and Diplomacy.
“The constitution—and the law here—is not clear as to whether or not the president” has authority to exit such an agreement. “You’re going to get some justices saying this is a political question for the Congress and the president to work out”: Richard Walawender, head of law firm Miller Canfield’s international practice.
“If he proposes to terminate, the reaction in both Mexico and Canada would be awful. Agriculture in particular would go ballistic, the auto industry would go ballistic”: Fred Bergsten, a senior fellow at the Peterson Institute for International Economics.

No matter who’s right, withdrawal undoubtedly would trigger some serious pushback from lawmakers and lobby groups for farmers and car makers, which have enjoyed significant benefits from the 23-year-old deal. Hofstra University’s Ku speculated that a business or industry group that depends on the agreement would sue to keep it intact.

“They would have the resources to fight it all the way to the Supreme Court,” he said.