US trade officials finalized steep tariff levels on most solar cells from Southeast Asia, a key step toward wrapping up a year-old trade case in which American manufacturers accused Chinese companies of flooding the market with unfairly cheap goods.

The US Commerce Department has announced plans to impose tariffs of up to 3,521% on imports of solar panels from four South East Asian countries. It comes after an investigation that began a year ago when several major solar equipment producers asked the administration of then-President Joe Biden to protect their US operations.

The U.S. announced tariffs on Malaysia, Cambodia, Vietnam, and Thailand on Monday, capping a yearlong trade probe initiated under the Biden administration.