My lawyer sister in law told me if that if potential new company calls to verify/check references, old company legally is only allowed to answer whatever questions they are asked. So if new company says “Did Joe work for you for 5 years?” Old company is supposed to say yes, and that’s it. But if new company asks a specific question such as “why was Joe terminated?” Then old company is legally allowed to answer. Basically past employers are not allowed to bad mouth you unless they are specifically asked questions that validate negative information being shared, they cannot offer negative info without being asked about it. I hope that makes sense. PS I’m in CA, no clue if laws vary by state.