What should my husband do if his boss is stealing hours from him at work? He clocks in and works overtime and his paycheck doesn't reflect that.

The time clock at my husband job is the type where you clock in with your fingerprint. He and his other coworkers are having the same issue with their paychecks as well. They feel they're being robbed as well. They have complained and filed grievances with their union, but it falls on deaf ears because their union does not help, so they're at a loss of what to do. Their boss is always threatening their jobs every time they question things. They're all Hispanic. Also, all the Hispanic workers are not allowed to use the bathroom, only the white workers are allowed the use of the bathroom. The Hispanic workers must relieve themselves in the tipping floor outside like animals. Not only is it illegal, but unsafe. They work for a garbage transfer station. Every time my husband mentions OSHA, the boss threatens his job. So please help with any advice. The union is not helping. As long as the boss hands them an "envelope", they turn the other cheek. What can the workers do?