What to do if you haven't received wages for working!`

My son works for a company who has been paying him by check bi-weekly for the extent of time he has been employed. Recently he has not received his paycheck plus he has overtime hours that he hasn't been paid for. He is almost owed two paychecks, which equals out to a months worth of work. What can he do about this? I figured since he is paid by check that there is someone he can contact to report this employer. I would appreciate it if you can steer us in the right direction. He just recently rented an apartment and is expecting a baby in September. He is very worried about his circumstances and continues to go to work in hopes that his employer will pay him. To my knowledge this employer is not paying any of their employees.