A federal program that checks the immigration status of job applicants adds costs to the hiring process and reduces the pool of workers, some business owners say. Use of E-Verify is required for at least some businesses in at least 16 states and could soon become a mandate under legislative efforts to overhaul immigration. A February survey from U.S. Citizenship and Immigration Services showed that out of 1,351 employers that use the system, 85% would continue using E-Verify for hiring even if it is not required.