U.S. officials have begun blocking the import of solar panels that they believe could be products of forced labor in China, implementing a recent ban that could slow the construction of solar-energy projects throughout the country. Industry executives and analysts said solar panels from at least three Chinese companies have been targeted in recent weeks, and a Customs and Border Protection spokesman confirmed by email that the agency has “made a number of detentions” of products under the import ban.

CBP imposed the ban in June on Hoshine Silicon, which produces raw materials used in solar panels. The agency said it had information “reasonably indicating” that Hoshine, which operates plants in China’s Xinjiang region, uses forced labor, a finding that triggered the ban because U.S. law prohibits the import of goods made by coerced workers.

Hoshine had been linked by The Washington Post and human rights researchers to coercive state labor programs targeting Uyghurs and other minorities.

Chinese companies dominate global production of solar panels, with many using raw materials from Hoshine, the world’s largest producer of metallurgical-grade silicon.

Solar is the fastest-growing source of new electricity generation in the United States, according to the Biden administration, which is aiming to boost it from 3 percent of electricity generation today to more than 40 percent by 2035.

The ban brings to the fore the tension between the administration’s human rights agenda and its efforts to address the climate crisis.“We want to rapidly transition our fuels to solar and wind and other renewables,” said Mark Z. Jacobson, a renewable-energy expert and engineering professor at Stanford University. “Any slowdown of this transition creates a loss of life,” he added, noting that the burning of fossil fuels is the main driver of air pollution that causes 78,000 deaths per year in the United States and 7 million globally.

Homeland Security Secretary Alejandro Mayorkas, who oversees CBP, has said the administration remains committed to renewable energy. “But, and this is very important, we’re going to root out forced labor wherever it exists, and we’ll look for alternative products to achieve the environmental impacts that are a critical goal of this administration,” he said when he announced the import ban in June.

The CBP enforcement actions have “had a real significant disruption to a lot of planned projects and their ability to complete them this year. It’s going to be very challenging, very difficult,” said Mark Widmar, chief executive of First Solar, a U.S.-headquartered panel manufacturer that doesn’t use Chinese materials.

Widmar said he’s been contacted by some customers looking for alternative suppliers because they’ve had panels detained. First Solar is building new factories in Ohio and India but has limited capacity to fulfill new orders in the coming months, he said.