The Trump administration says it would have to refund up to $1 trillion in customs revenue if it loses a tariff case before the Supreme Court and the opinion doesn’t arrive until June.

The U.S. has collected nearly $160 billion in tariff revenue this year, though President Trump recently finalized high levies on imports from dozens of countries that should supercharge collections in the coming months.

Treasury Secretary Scott Bessent is warning that it may have to refund it if the Supreme Court upholds a lower court ruling that says Mr. Trump overstepped his powers in issuing country-by-country levies.

“For example, delaying a ruling until June 2026 could result in a scenario in which $750 billion-$1 trillion in tariffs have already been collected, and unwinding them could cause significant disruption,” Mr. Bessent wrote to the Supreme Court.

Mr. Bessent estimated the refund last week in a court filing that requested expedited review of the case. The administration would like to have an oral argument before the justices by November.

The Treasury secretary says there is no time to lose. Other countries will be wary of dealing with his team, he said, after an appellate panel said Mr. Trump unlawfully imposed blanket tariffs on dozens of trading partners.

“The recent decision by the [U.S. Circuit Court of Appeals for the] Federal Circuit is already adversely affecting ongoing negotiations. World leaders are questioning the president’s authority to impose tariffs, walking away from or delaying negotiations, and/or imposing a different calculus on their negotiating positions,” Mr. Bessent wrote. “The longer a final ruling is delayed, the greater the risk of economic disruption.”

Mr. Trump struck a series of deals with trading partners, but the White House is working to finalize the agreements. It recently finalized a deal with Japan that calls for massive investments in the U.S., and a trade team from South Korea is in Washington this week to pin down details of their pact.

The pending case stems from a lawsuit that blue states and small, import-reliant businesses filed against Mr. Trump over his “Liberation Day” tariffs on dozens of nations. They said he usurped powers typically reserved for Congress by declaring a national emergency and claiming the right to impose tariffs on any country under the International Emergency Economic Powers Act of 1977.

“It seems unlikely that Congress intended, in enacting IEEPA, to depart from its past practice and grant the President unlimited authority to impose tariffs. The statute neither mentions tariffs — or any of its synonyms — nor has procedural safeguards that contain clear limits on the President’s power to impose tariffs,” the circuit court said in its ruling.

Mr. Trump says forfeiting the tariffs would make the U.S. “unbelievably poor again.”

Tariffs are a duty, or tax, on goods that are brought into U.S. markets from foreign nations. Importers, often U.S. companies, pay the tax and not foreign nations.

The U.S. is collecting outsized revenue because Mr. Trump imposed a blanket 10% tariff on all imports earlier this year.

He recently finalized tariffs from 15% to 41% on dozens of countries, raising levies to their highest levels in over a century.

Besides revenue, Mr. Trump says tariffs give him leverage over other nations and will benefit American workers by forcing companies to set up shop in the U.S. to avoid the levies.

“The stakes in this case could not be higher,” U.S. Solicitor General D. John Sauer wrote in a brief to the Supreme Court. “The president and his Cabinet officials have determined that the tariffs are promoting peace and unprecedented economic prosperity, and that the denial of tariff authority would expose our nation to trade retaliation without effective defenses and thrust America back to the brink of economic catastrophe.”

The case deals with so-called reciprocal tariffs that Mr. Trump imposed to rebalance trade with other nations, plus drug-trafficking related levies he imposed on Mexico, Canada and China.

Sector-specific tariffs on cars, steel and aluminum were imposed under alternate authorities and are not at risk in this legal fight.

• Tom Howell Jr. can be reached at thowell@washingtontimes.com.