Illegal Aliens: Significant Obstacles to Reducing Unauthorized Alien Employment Exist, Statement of Richard M. Stana, Associate Director, Administration of Justice Issues, General Government Division, before the Committee on the Judiciary, Subcommittee on Immigration and Claims, House of Representatives [open pdf - 80KB]
"One of the primary magnets attracting illegal aliens to the United States is jobs. Immigration experts believe that as long as opportunities for employment exist, the incentive to enter the United States illegally will persist, and efforts at the U.S. borders to prevent illegal entry will be undermined. Therefore, these experts believe that reducing the availability of employment for illegal aliens should be an integral part of a comprehensive strategy to reduce illegal immigration. […] The Immigration Reform and Control Act (IRCA) of 1986 made it illegal for employers knowingly to hire unauthorized aliens. IRCA requires employers to comply with an employment verification process intended to provide them with a means to avoid hiring unauthorized aliens. The process requires newly hired employees to present a document or documents that establish their identity and eligibility to work. Employers are to review the document or documents that an employee presents and complete an Employment Eligibility Form, INS Form I-9. On the form, employers are to certify that they have reviewed the documents and that the documents appear genuine and relate to the individual. Employers are expected to judge whether the documents are obviously fraudulent. IRCA also provides for penalties or sanctions, such as fines, against employers who do not complete the verification process or who knowingly hire unauthorized aliens. INS, under its worksite enforcement program, and to a limited degree, Labor, are responsible for checking employer compliance with IRCA's verification requirements."
Government Accountability Office (GAO): http://www.gao.gov/