The Commerce Department has slapped stiff tariffs on imports of Chinese solar panels, imposing 31 percent charges on the products of big Chinese manufacturers like Suntech and Trina. The duties will be retroactive for 90 days.

The preliminary import duties were the result of a dumping case brought by a group led by SolarWorld, the U.S. subsidiary of a German company. The group said Chinese solar panel makers had violated World Trade Organization rules, using unfair cost advantages and selling panels in the United States at below-cost prices to drive U.S. manufacturers out of business. The duties will be reviewed again at the end of the year.

“The verdict is in,” Gordon Brinser, president of SolarWorld, said in a prepared statement. “In addition to its preliminary finding that Chinese solar companies were on the receiving end of at least 10 WTO-illegal subsidies, Commerce has now confirmed that Chinese manufacturers are guilty of illegally dumping solar cells and panels in the U.S. market.”

 However, the case has divided the solar industry in the United States. U.S. makers of solar manufacturing equipment and U.S. firms that install solar panels said import duties would raise solar costs in the United States, shrink the U.S. market and hurt U.S. jobs. About half of the solar panels installed in the United States last year were made in China.

“We will fight SolarWorld’s anti-consumer and anti-jobs effort,” said Jigar Shah, founder of Sun Edison and president of the Coalition for Affordable Solar Energy . A study commissioned earlier by the coalition had said that a 50 percent tariff would eliminate 14,000 jobs in the United States and Shah said the actual 31 percent tariff would also cost thousands of jobs.

Shah said he also feared that China would pursue a trade case against U.S. exporters of polysilicon, a key component for making solar panels. “What we’re worried about is a full -fledged trade war,” Shah said.

But Steve Ostrenga, chief executive of Helios Solar Works, said in a statement that the Commerce decision “underscores the importance of domestic manufacturing to the U.S. economy and will help determine whether the country will be a global competitor in clean technologies or outsource them China.”