In the United States, free speech principles as they apply to defamation law basically allow anyone in your former company to say TRUTHFUL things about your PUBLIC behavior in the workplace without fear of legal liability. But because most employers are allergic to lawsuits, they generally advise their employees to say NOTHING other than verifying dates of employment (to prevent employees saying illegal things about their former colleagues like what race or religion they are, for example). But if you actually phone up references, many of them are quite talkative. Whether they follow the boss's advice not to say much is on them. And a really wonderful way to use references (which I did, as a community volunteer advised by a professional search firm for my local school district many years when it was hiring a new superintendent) is to call and ask for BACK references, that is "Who else do you know who could comment on how well Mr. Smith could do this job he is applying for?" That is perfectly legal, and very informative.