Employment Law Questions? Ask an Employment Lawyer.
Unless you can state that the harassment is based on your race, religion, gender, age, disability or recent FMLA use, there is nothing that can be done in an employment law sense. If you can state that one of those in the basis for the harassment, you should immediately file an EEOC complaint in your state.
However, even if you can't allege discrimination, you can sue the individual that is making false statements about you for defamation of character. You can hire a local attorney to send a "cease and desist" letter first, and if that doesn't work, you can file a small claims lawsuit as a means of some recovery. Typically, when someone gets a cease and desist from an attorney, that convinces them to stop lying about you.