Information on DOL complaints can be found at:
https://www.eeoc.gov/youth/who-can-file-complaint
I think there is a general lack of understanding about what our rights are as workers, and an assumption that it is nearly impossible to file a DOL or EEOC complaint when workers' rights have been violated. This misunderstanding of workers' rights is compounded by the use of staffing agencies. Federal law is very clear. Both the staffing agency and the client (company) are responsible for maintaining lawful compliance with all labor laws.
If you think you have had your rights violated, filing a claim is easy. And, you don't need proof. Also, if your employer retaliates, that in and of itself is a very serious labor code violation and you can submit another complaint. Complaints are investigated by the DOL/EEOC and if found in your favor, result in financial compensation (among other things).
If the complaint is investigated and the result is not in your favor, nothing happens. It doesn't cost you any money. It doesn't take but 10-15 minutes, and literally nothing happens if it is decided that the situation doesn't arise to the level of a labor code violation.
You do not need proof. And, you do not need to know if it actually is a labor code violation or not. You do not even need to be certain that what happened was illegal. And, if you have a complicated employment situation, such as being hired through a staffing agency, you do not need to know exactly who to hold responsible. The investigating agency will figure out all of that for you and will even advocate on your behalf. You only need to tell your side of the story.
If you suspect that your rights have been violated for any reason in the past 2 years, it is time to file a complaint.
For wage and hour claims:
https://www.dol.gov/agencies/whd/contact/complaints
For violation of your civil rights, discrimination based on sexual orientation/identity, race, age, disability, or similarly perceived protected classes, instructions and complaint form: