My employer doesn't pay overtime to the kitchen staff, About 20 hrs. a week each to four people, Any ideas???

Is there recourse? This has been going on for years .. He gives them straight pay of Approx. $12.00 Hr. So this obviously would be $18.00 Hr if O.T. The staff are legal and put up with his intimidating antics, plus he has not given a raise in almost 7 years.And to add insult to injury his business is a cash cow and he owns several houses and fine cars. I don't work for him anymore and can't stand the guy at all,, I'd love to screw him over like he's been doing to others.. Any ideas?