U.S. Customs and Border Protection will immediately halt shipments from the Hoshine Silicon Industry Co. Ltd. and its subsidiaries under a law that bans the import of goods produced with forced labor.

In addition, the Commerce Department will add six Chinese entities involved in the production of raw materials and components for the solar industry to a blacklist barring them from access to the American market, the administration said.

The moves target a relatively small slice of the U.S. import market, but could make it harder to achieve the administration’s renewable energy goals. It reflects an escalation of efforts to use economic leverage to pressure China over its use of forced labor as part of its campaign against ethnic minorities in the country’s far wester Xinjiang region.

“Our environmental goals will not be achieved on the backs of human beings in a forced labor environment,” Homeland Security Secretary Alejandro Mayorkas said. “We are going to root out forced labor and we are going to use alternative products that are manufactured legitimately in keeping with our values and our commitment to a fair market place.”

CBP found evidence that workers there intimidated, threatened and their movement was restricted in its investigation of the of the polysilicon industry in Xinjiang, officials said at a news conference.

The U.S. previously banned cotton and tomato imports from Xinjiang amid evidence of forced labor as part of China’s forced assimilation campaign targeting predominantly Muslim minorities in the region, which the Chinese government has denied.

The effort to put increased economic pressure on China over the situation in Xinjiang has been gaining momentum in recent months. Canada and Britain have moved to restrict imports over the issue and the Group of Seven major industrial nations agreed at its recent summit to ensure global supply chains are free from goods made under conditions that are akin to modern slavery.

China denies allegations that it uses forced labor in Xinjiang or elsewhere and has broadly rejected the consistent and well-documented reports that Uyghurs and other minorities have been detained under brutal conditions, subjected to indoctrination and intensive surveillance intended to force them to assimilate into the dominant Han culture.

Members of Congress have for months urged the U.S. to ban Xinjiang-sourced polysilicon, which is used to manufacture the cells that are assembled into solar panels, and some type of enforcement action was expected.

CBP is still investigating the extent of Hoshine’s involvement in the U.S. market but direct shipments over the past 2 1/2 years totaled about $6 million while finished goods that include material from the company were about $150 million, said Ana Hinojosa, who runs the agency’s trade enforcement team.

That’s a relatively small amount. Solar panel imports totaled about $7 billion last year, comprising about three-quarters of the overall U.S. market, according to the Solar Energy Industries Association.

Chinese panel manufacturers have largely been shut out of the U.S. market by tariffs. Imports predominantly come from Malaysia, South Korea, Vietnam and Thailand. Those panels, however, could still include wafers made with polysilicon from Xinjiang, though the industry has been working to audit and remove the material from the supply chain, said John Smirnow, general counsel and vice president of market strategy for the association.

“The end customers want to make sure that the solar panel that’s going up on their roof is free of forced labor,” Smirnow said.