The US set duties on imported solar cells from China on Tuesday, after investigating complaints from US competitors that Beijing provides manufacturers significant subsidies.
The Department of Commerce said it would immediately begin collecting duties on Chinese-made crystalline silicon photovoltaic cells, and modules assembled from the cells, to offset subsidies for producers that run from 2.9 percent to 4.7 percent.
The main firms hit by the preliminary ruling, it said, were Suntech Power, the world's largest maker of solar panels, and Trina Solar energy, another leading producer. A final ruling will be issued in June, it said.
The department said a parallel investigation into whether Chinese producers are dumping underpriced solar cells into the United States is continuing and a ruling will be announced in two months.
Additionally it ruled that solar panels produced in other countries using Chinese-made solar cells could also be subject to anti-dumping and anti-subsidy duties.
US companies have accused China of improperly subsidizing its solar sector as part of a no-holds-barred commercial battle for supremacy over an industry experts estimate will be worth trillions of dollars in the future.
Also on Tuesday the Commerce Department confirmed steep anti-dumping and anti-subsidy duties set on galvanized steel wire from China and Mexico and on brightening agents used in paper production from China and Taiwan.
The duties were first set last year under a preliminary ruling.
The moves come as the US steps up efforts to protect domestic manufacturers from Chinese imports that it alleges benefit from deep subsidies and an artificially undervalued currency.
In February President Barack Obama took direct aim at China's huge trade surplus with the United States when he ordered the creation of the Interagency Trade Enforcement Center to expedite unfair trade complaints from US business.