My previous employer is giving bad references about me, what can I do?

There is a statute outlawing employers saying false, negative things about ex-employees. However, if the things he is saying are true, or if they are mere opinions (he wasn't a good worker) then that's not illegal. Have a friend call pretending to be a prospective employer asking for a reference and see what he is saying. Then have a lawyer write a cease and desist letter advising the employer that what he is doing is illegal and that you have a witness. That should stop him.

Most employers will only verify dates of employment, salary and eligibility for rehire. They do this to avoid potential liability from defamation claims. If you can prove your employer is providing false information, you may have a defamation claim. If the "bad" reference is factually true, there is not much you can do.