An employer asked about a former employee faces two risks: defamation for inaccurate negative statements, and negligent misrepresentation for incomplete positive ones.
Defamation requires a false statement of fact published to a third party causing harm. Opinions and true statements are not actionable, though the line between opinion and implied fact is thin in practice.
Qualified privilege protects communications made in good faith on a subject in which the speaker and recipient share a legitimate interest — which ordinarily covers reference-giving. It is lost by malice, knowledge of falsity, reckless disregard, or excessive publication to people with no interest.
Statutory immunity exists in many states for employers providing job performance information in good faith, sometimes with a presumption of good faith the plaintiff must rebut.
Self-publication defamation, recognised in a minority of states, allows a claim where the employee is compelled to repeat the employer’s stated reason to prospective employers.
The practical policy. Route all reference requests to one function; confirm dates, title and, where policy permits, salary; and require a signed release before saying more. Where a release is provided, be accurate and stick to documented performance.
Consistency matters more than content. An employer that gives warm references generally and silence for one person has said something.