If they crossed the border illegally they have already broken the law.
If they are working in the US they have already broken the law.
If thy are being paid under the table they are breaking g the law.
If they are driving without a drivers license, they are breaking the law.
If they were deported and re-ntred the US they have broken the law.
False Personation of a U.S. Citizen (18 U.S.C. § 911). Illegal aliens often present themselves as U.S. citizens, an act punishable by up to five years in jail, a felony. This law is often cited in immigration prosecutions and may involve, for example, an alien claiming U.S. citizenship to his employer.
Fraud and False Statements (18 U.S.C. § 1001). It is common for illegal aliens to make false statements to the government or on official documents. An illegal alien violates this law when claiming to be a U.S. citizen on an I-9 Employment Eligibility form and faces a fine and up to five years imprisonment.
Social Security Fraud (42 U.S.C. § 408). This statute has been invoked where an illegal alien provided a false Social Security number for the purpose of acquiring a job, where an illegal alien used a fraudulent Social Security number for the purpose of acquiring a driver's license, and when an illegal alien used a Social Security card belonging to a citizen in order to obtain Section 8 housing, for example. Violation of this statute can result in a fine and/or imprisonment up to five years. The court can also require violators to provide restitution to the victims.
So what's the hold up? Waiting for another law to be broken???