It’s not a new opinion from Piper, necessarily—the bank laid out its reasoning in April, shortly after Trump’s “Liberation Day” announcement of universal tariffs under the IEEPA. Then, as now, it sees a 9–0 ruling in the Supreme Court against Trump as more likely than a Trump win.

After Trump announced the sweeping tariffs against “friend and foe” alike on April 2, analysts had been concerned about the “smell of stagflation,” a toxic mix of stagnant growth and rising inflation. Immediately afterward, they were unanimous in declaring them a disaster. They didn’t all focus on the questionable legality of the tariff regime, though. Earlier this month, [http://Trump’s tariffs are turning into a ‘mosaic’ that will be ‘idiosyncratic,’ Morgan Stanley says, projecting a $2.7 trillion haul over 10 years]Morgan Stanley called them a “mosaic” and “idiosyncratic,” and projected them collecting $2.7 trillion in revenue over 10 years.

The reason that the Piper Sandler team of Andy Laperriere, Don Schneider, and Melissa Turner is revisiting the subject is that oral arguments in these and similar cases are scheduled through September. The U.S. Court of Appeals for the Federal Circuit will hear oral arguments on whether Trump truly has unlimited authority under the IEEPA to impose tariffs on Thursday, July 31. Piper Sandler forecasts that appellate courts will issue rulings over the next several months.

“Trump will probably continue to lose in the lower courts, and we believe the Supreme Court is highly unlikely to rule in his favor,” the bank said. Here’s why.

Stiff resistance

Trump’s trade policy has encountered stiff resistance as lower courts push back against the administration’s sweeping claims of executive authority. On May 28, the U.S. Court of International Trade (CIT) ruled unanimously against Trump’s use of the IEEPA for tariffs, calling the administration’s arguments unconvincing. The decision is now under appeal.

In a separate May 29 ruling, D.C. District Judge Rudolph Contreras found that the IEEPA does not enable the president to impose tariffs at all and ordered an immediate reversal of certain duties—though that order is currently stayed pending appeal.

According to Piper Sandler, the heart of the matter is congressional intent. As it did in April, the firm argues that the IEEPA, enacted in 1977, was designed to give the president certain emergency economic powers, but not blanket authority to set tariffs. Courts have consistently rejected the idea that the statute includes such sweeping power.

If the Supreme Court rules against Trump, all trade deals and announced tariff changes made under the IEEPA—including minimum 10% import rates and threatened reciprocal tariffs—would be declared instantly illegal. Refunds could flow to companies and individuals who have paid unlawfully imposed tariffs, if they file claims with the CIT.

Tariffs are likely to remain in place in the near term, supported by administrative stays and the slow judicial process. Even if reciprocal tariffs are struck down, Trump could pivot to other statutes, such as Section 232 (covering steel, aluminum, and cars), though these have even stricter legal guardrails and could invite further litigation.

There are at least eight ongoing lawsuits from a diverse range of plaintiffs—including states, tribes, and small businesses—all challenging Trump’s use of the IEEPA. Court dockets now stretch across several federal circuits, suggesting years of legal battles to follow, even if Trump loses at the Supreme Court.

Still, with Trump’s well-known litigious nature, and the legal calendar ahead, Piper concludes: “Instability surrounding trade is likely to last a lot longer.”

[This report has been updated with regard to length and brevity.]

For this story, Fortune used generative AI to help with an initial draft. An editor verified the accuracy of the information before publishing.