America’s largest companies are already facing a backlash from the passage of a new U.S. law that severely restricts imports from the Xinjiang region in China, where the U.S. government and human rights advocates say businesses use forced labor to produce essential building blocks of the modern global economy, like cotton-based fabrics and silicon. Walmart Inc. WMT, +1.14% , the world’s largest retailer, is the latest in a series of U.S. firms that have been criticized on Chinese social media amid pressure under the new law to rid its shelves of products that have been made with parts from the…