President Donald Trump has threatened to levy a new 50 percent tariffs on goods from countries that provide weapons to Iran, but top economic advisers aren’t on the same page on how the president could accomplish that.

White House National Economic Council Director Kevin Hassett suggested Thursday morning that the president can use a 1977 emergency law, despite the fact that the Supreme Court ruled in February that statute does not authorize tariffs.

“This is clearly within the president’s tariff power, that if we’re in a state of conflict, then the IEEPA policy is exactly designed for that,” Hassett said on Fox Business with Maria Bartiromo, using the acronym for the International Emergency Economic Powers Act. “Countries really should be careful. If you’re helping our adversary, then President Trump will take note and he’ll take action.”

But U.S. Trade Representative Jamieson Greer threw cold water on that idea hours later, telling POLITICO at a stop in Michigan that the law could be used to “prohibit” certain trade — say with an embargo — but “not so much for tariffs.”

“You can have the same effect with IEEPA as a prohibitive tariff,” Greer added, noting that other tariff authorities remain available and that he is “still reviewing options with the president” for imposing the 50 percent duty.

Asked about Hassett’s comments, a White House official said, “The President has numerous executive powers at his disposal to safeguard our national security, including IEEPA. The administration is exploring all available tools to ensure both Americans and the world are safe from any terror threats.” The official, who was granted anonymity to discuss the administration’s strategy, did not immediately respond to a follow-up question about Greer’s comments.

The remarks come a day after Trump posted on social media that he will impose steep tariffs“immediately” on any country that supplies military weapons to Iran, saying the duties would carry “no exclusions or exemptions.”

The Supreme Court decided on Feb. 20 that IEEPA does not authorize the president to impose tariffs without Congress’ approval, striking down double-digit duties the White House set on goods from dozens of countries last year.

The Trump administration had argued the law, which allows the president to regulate economic activity during national emergencies, should be read to include tariff authority by relying on earlier wartime precedents, when presidents exercised broad control over the economy, even though the U.S. wasn’t at war when Trump imposed his duties.

The Court rejected that argument, saying it was not “persuaded that the dots connect from our wartime precedents … such that IEEPA should be interpreted to grant the President an expansive peacetime tariff power,” and concluding that “the historical argument based on the Court’s wartime precedents fails.”

But the justices did not directly address whether IEEPA operates differently in an actual wartime scenario.

That may leave open a narrow legal possibility during an active conflict, said Ed Gresser, a former USTR economist now at the left-leaning Progressive Policy Institute. Gresser cautioned that the theory would be difficult to apply in the current situation, however, noting the administration has not sought congressional authorization for the use of force to strike Iran over the past five weeks. “I don’t see how they can square that with a claim that, because we’re in a state of conflict, the administration can use IEEPA to impose tariffs,” he said.

Peter Harrell, a White House economic adviser under former President Joe Biden, was also skeptical. “I’m sure that if Trump actually tried to impose tariffs here, they’ll be tied up in litigation for quite some time, and I am skeptical that the government would prevail,” he said.

The Trump administration could also try to tap other trade laws to justify a 50 percent tariff on countries selling weapons to Iran, though those would also be a legal stretch and would not be immediate.

“He’d really be better off just imposing sanctions here, which clearly are legally allowed,” Harrell added.

The Trump administration has already begun rebuilding its tariff regime following the court’s ruling, including setting a flat 10 percent tariff using Section 122 of the Trade Act of 1974, which allows duties of up to 15 percent for 150 days to address a “large and serious” balance-of-payments deficit. Two groups have already challenged those duties in court.

Greer has also launched new investigations under Section 301 of the Trade Act of 1974 that could lead to tariffs on dozens of countries, and is expected to roll out additional sector-based tariffs under Section 232 of the Trade Expansion Act of 1962.

White House advisers send mixed messages on Trump's latest tariff threat