What can acurrent employer say to a prospective employer?

An former employer is not limited the merely the discussion of "basic" information.  Unfortunately, there is no action against a former employer for a negative response to a prospective employer's inquiry.  The law provides what is called a "qualified privilege" for answers to pre-employment inquiries. This guarantees that companies will be free to answer these-type questions fully without fear of a lawsuit. This means that a former employee can only sue for willful or reckless remarks; that is for things that are false and grossly untrue.  In any event, it's often very hard for a former employee to prove what is being said about them by a past employer.  Also, even without the privilege certain statements are legally allowed. For example, statements of fact aren't legally actionable; therfore saying that they would not re-hire you can't be defamatory because they can prove it's true.  Additionally, statements of opinion aren't a basis for a lawsuit. So if your former employer said, "X uses drugs" that is a statement of fact that may be actionable if untrue; however saying that, "I think X is the worst worker I've ever supervised" is a statement of opinion that may be hurtful and unfair, but does not constitute the basis for claim.  Bottom line, in order to sue for defamation, the information must be a false statement of fact.   Again, without more details it's hard to say.  If you think that your previous employer has defamed you, you should consult with an employment law attorney in your area.