That's up to you to disclose.

Any HR rep with half a brain isn't going to divulge employee/company details because they know when X employee finds out they are likely going to get sued for defamation.

Having said that, like others posted it's not illegal for them to disclose certain information on you, but it better be accurate. It's not defamation if it's true, but if they can't prove that concretely that's gonna be libel/slander in civil court.

Individual states will also have different laws concerning this.

Most corporations aren't willing to risk it which is why they direct their HR reps/managers to only verify employment dates, positions, and salaries.