What should I do if my employer owes me overtime pay for the last 4 years?

It is essential, that you contact an attorney with experience and a thoroughly up to date understanding of this complicated and ever changing area of lawand you should do so as soon as possible, because time is literally money for a former employee attempting to collect overtime wages. The timing is crucial because each week you wait, you will likely be unable to collect the overtime and other damages that should have been paid to during the week you worked the hours. (You can only collect overtime for a period ranging back 3 years from the time the lawsuit is filedbefore the lawsuit is filed the clock on those years is ticking away week by week; and please understand that filing a claim with the Department of Labor does not stop that clock, only a complaint in court does) Yes, you should absolutely sue, presuming you have been working over 40 hours a week, have been paid time and one half, and do not meet any exemption to relevant statutes. If the above can all be proven you will be entitled to double the amount of wages you underpaid for at least the previous two years, and possible the previous 3 years. Your employer will also be responsible for all the costs of litigation, attorney's fees (even though you do not have pay the attorney's fees). Moreover, there are likely other employees and former employees who have also been underpaid, and if the word got out, or if you decided you wanted to include them in your lawsuit, your employer could face serious financial consequences.