Answer 1

E-Verify is an electronic program through which employers verify the employment eligibility of their employees after hire. The program was authorized by the Illegal Immigration Reform and Immigrant Responsibility Act of 1996 (IIRIRA). In short, employers submit information taken from a new hire's Form I-9 (Employment Eligibility Verification Form) through E-Verify to the Social Security Administration and U.S. Citizenship and Immigration Services (USCIS) to determine whether the information matches government records and whether the new hire is authorized to work in the United States.  

You can find more info from the USCIS' website:
https://www.uscis.gov/e-verify

Answer 2

E-verify是美国政府为了监测公司没有雇佣非法员工的一个Program。公司需要承诺移民局每次雇佣一个新的员工的时候都会把新员工的工作许可信息在移民局的网站上Verify，让系统来监测这个员工是否可以合法的工作。Enroll进E-verify是免费的，但是录入每个员工的信息需要手动完成，因此很多雇主不愿意参与这个Program。