WASHINGTON—Two U.S. senators have asked the leading solar energy lobbying group to clarify U.S. dependence on solar products linked to forced labor in China’s Xinjiang, part of a push in Congress to address what Western countries say are rights abuses by Beijing. Republican Marco Rubio and Democrat Jeff Merkley sent a letter on Tuesday asking the Solar Energy Industries Association (SEIA) to detail measures it or member companies have taken to ensure that solar products sourced from Xinjiang, including polysilicon, are not made using forced labor. The senators asked SEIA for information on “the extent to which the U.S. solar supply chain is currently dependent” on polysilicon and solar ingots/wafers made in Xinjiang, according to a copy of the letter seen by Reuters. Polysilicon is the key raw material used to produce solar panels that generate electricity from sunlight. In the letter, the senators said that reliance on a China-based …