You can try contacting the state department of labor, to see if they will help--they do with many wage cases, so they might also help with improperly withhold tips. If they won't, then your only option is to sue your employer (in say, small claims court, where you can act as your own attorney, or "pro se," to save legal fees) for the money. You sue for breach of contract: there was an agreement (even if only an oral or unwitten one) pursuant to which you were paid and received tips for work; you did you work, so the employer was obligated to pay you.