The complaint filed in the U.S. Court of International Trade in Manhattan argued that the president's invocation of the act beginning in February illegally imposed tariffs on goods imported from Mexico, Canada, and China. Trump has said that tariffs were justified as a matter of national emergency because of the amount of fentanyl making its way into the United States from those countries, and that the global levies are a necessary tool to negotiate trade deals that level the playing field between the United States and key global trade partners.

The U.S. Supreme Court heard oral arguments regarding Trump's authorization to invoke the IEEPA in early November. The issue has been fast-tracked, but the justices have not announced when they intend to make a ruling. Costco's complaint requests a complete refund of duties it has already paid if the Supreme Court decides that the tariffs are unlawful.

Additionally, Costco is seeking "an injunction preventing Defendants from imposing further duties on it under the executive orders challenged in this lawsuit; and full refund from Defendants of all IEEPA duties Plaintiff has already paid to the United States as a result of the executive orders challenged in this lawsuit, as well as those it will continue to pay," its lawyers wrote.

The complaint was filed after Costco was denied a request for additional time to finalize its tariff calculations assessed on imported goods. That decision could impact the company's ability to collect a refund in full if the tariffs are invalidated, the company's lawyers argue.

The lawsuit does not say how much Costco has paid in tariffs; however, revenue from tariffs has soared throughout the year. For fiscal year 2025, the federal government collected nearly $196 billion in duties, taxes, and fees—a 122 percent increase from the prior fiscal year.

On Aug. 29, the U.S. Court of Appeals for the Federal Circuit ruled in a 7-4 decision that Trump's global tariff policies were illegal, sending the case to the nation's highest court. The tariffs remain in place while the justices consider the case.

More than a dozen states have sued the Trump Administration over the president's tariff policies. In April, Arizona, Colorado, Connecticut, Delaware, Illinois, Maine, Minnesota, Nevada, New Mexico, New York, Oregon, and Vermont filed suit against the president, arguing that only Congress has the power to enact tariff policies. California filed a similar suit.