An employer has to be paying "under the table" to have long term illegal employees. Only by paying cash and not reporting the expense can an employer keep from getting in trouble with the government unless, of course, if someone reports them.  Contract labor expense where an employee's name does not have to be reported only goes to about $600. An employer can take an employee's "green card" information while having a good idea that the information is false. When the government comes back and says the information is false, the employee has to be terminated. Thus for an employer to get caught having illegal employees is irresponsible, reckless and obtuse.