While most people who give this advice may be well meaning, it is meaningless for many people and can even be bad advice at times. Note: this is USA specific.
In the US, the only “labor boards” that exist are the National Labor Relations Board and much more rarely, a state Labor Board that handles non-NLRB jurisdictions (like farm labor or public sector work). These boards protect an employees right to engage in concerted activity to better working conditions. For example, the board will act if at least 2 employees complained about working conditions, went on strike, tried to join a union, and the employer retaliated.
If you were paid late, less than overtime, or less than minimum wage, contact either the Department of Labor or a state/local wage and hour agency. You should also consult an attorney, who will likely take a case on contingency if it's any good.
If you were discriminated based on membership of a protected class, talk to a lawyer FIRST and as soon as possible, then either file a charge with the EEOC or a similar agency at the local level.
If there are health and safety concerns at work, contact OSHA or a local/state version of that agency.
If you are denied access to restrooms or water, contact the local Health Department.
If you are retaliated for doing any of the above, contact the same agency or lawyer and they will help you.
This isn't all-inclusive, but hopefully gives people an idea of where they can seek recourse. And don't forget, unionize: collectively, we bargain, divided, we beg.