(Reuters) – China’s JinkoSolar Holding Co Ltd reported that some of its panels had been temporarily stopped at U.S. borders. The U.S. is concerned about solar panel production by Muslim minority groups from China’s Xinjiang province.

Jinko officials told Wall Street analysts during a Wednesday quarterly conference call that margins and profits were affected by the detainments. They did not divulge how much product was being held back U.S. Customs and Border Protection.

On Thursday’s conference call Haiyun Cao, Jinko director said that “we did have some modules blocked by the U.S. CBP” and requested additional documentations. “At the moment, we remain cautiously optimistic regarding the outcomes.”

Jinko representatives did not immediately reply to our request for further details. According to the company’s web site, the company ranks among the top panel producers in the world and has installed more than 14 gigawatts worth of panels across the United States. This is enough power to supply approximately 2.6 million homes.

CBP spokesperson declined comment Thursday on Jinko’s shipping.

As part of its efforts to hold China accountable in human rights abuses, the United States has banned all imports of products containing silicon metals that were sourced from China’s Hoshine Silicon Industry Co.

The key raw material for the solar industry, polysilicon is made from metallurgical silicon. Xinjiang is home to approximately 45% of the polysilicon that goes into solar module manufacturing.

China refutes claims that it is using forced labor in its solar companies.

The top U.S. trade organization for solar said earlier this week that the ban was “representing a significant and widespread downside risk to the industry’s optimistic forecasts.” The Solar Energy Industries Association stated that CBP searches into the detained equipment may cause significant project delays.