Unauthorized employment: 1) is a violation of nonimmigrant visa status; 2) can result in arrest and possible removal from the U.S.; 3) will result in a denial of an extension or change of status; 4) can be pointed to years later as an indication that a visa applicant committed visa fraud and is inadmissible to the U.S.; 5) if coupled with a false claim to U.S. citizenship, e.g. on an I-9 form, can lead to a finding of permanent inadmissibility with no waiver available.
I write this after counseling a man in F-1 student status and his wife in F-2 status, who hired an immigration attorney to do a PERM labor certification for him. The PERM and I-140 visa petition were successful. The attorney told them that, because of unauthorized employment, they could not adjust their status but would have to apply for their employment based visas in Poland. Unfortunately, the attorney did not inquire or advise them that the unauthorized employment which started before they did a change of status to F-1 actually made them ineligible for F-1 status, nor looked into the fact that they said on their I-539 Change of Status application that they had not worked. Now they are stuck, having paid thousands of dollars to an attorney for a process that is almost certain to fail. If a foreign national decides to engage in unauthorized employment, he or she should not seek a change or extension of temporary status.