Big U.S. companies are facing heightened scrutiny from Capitol Hill over their use of foreign employees on H-1B visas, with lawmakers raising concerns about layoffs and slumping job prospects for Americans. On Wednesday evening, Judiciary Committee Chairman Chuck Grassley (R., Iowa) and Ranking Member Dick Durbin (D., Ill.) sent letters to the country’s largest users of H-1B visas—including Amazon, Apple and JPMorgan Chase—asking them to explain why they continue to hire thousands of H-1B visa holders while also cutting other jobs. The senators asked for detailed information on how many H-1B workers the companies employ, what wages they are paid,...