Why not got one step further - the fines imposed on the employer could be set at the difference between the actual wage earned and the (minimum wage + $1/hour). The $1/hour/employee goes to the state bringing the prosecution to pay for the prosecution, the rest going to the employee. Punishment to fit the crime and it doesn't cost the tax payers to bring the prosecution.
Don't like it? Don't employee illegal immigrants, and pay your employees at least the minimum wage.