Legal Question in Employment Law in Illinois

Not enough information, but some basics are: if you are non-exempt (basically an hourly wage earner) and work specific hours and are not expected to be available due to a collective bargaining agreement or employment policy for other times, you should be able to earn money at a second job. If you are an exempt (salaried) employee, or a collective bargaining agreement or other place of employment policy requires you to be available at non-traditional times, yes the employer of the "full time job" can lay it on the line.