Valid work license? Issued only after checking for legitimate citizenship or intent to become a citizen after paying appropriate fees and/or fines?
Burden of proof will be on the employer.
Amazing how, almost two decades after the demise of communism and its system of rigorous control over its slaves (internal passports, work permits, state permission to relocate, et cetera), some folks want to put the shackles on their own wrists and ankles.