U.S. businesses that bought solar panels made in China earlier this year are retroactively being hit with unexpected tax bills, as they find themselves caught in the middle of a trade fight between U.S. and Chinese manufacturers.

The unusual bills are the result of action by the U.S. Commerce Department, which slapped provisional antidumping duties of between 31% and nearly 250% on solar panels containing Chinese-made solar cells in May.

The trade case has stirred tensions between Washington and Beijing and divided the U.S. solar industry. It is also resulting in large import-tax bills for dozens of U.S. companies, many small and medium-sized, that bought solar panels from Chinese suppliers as much as three months before the trade decisions were issued. The Commerce Department made the tariffs retroactive by 90 days.

Marco Mangelsdorf, who co-owns a company in Hawaii, ProVision Solar Inc., that designs and installs rooftop solar-panel systems, has been fuming since he received a tax bill in June from U.S. Customs, saying that he owed more than $138,000. That is 250% more than what he paid for a shipment of panels he received in February from a Chinese supplier.