>>>If some firm asked you your opinion about me and you'd give it (either negative or positive), without my approval or request for being a reference, I'd have bad feelings about it.
>>
>>Negative comments are illegal in the USA and Canada as far as I know.
>
>They aren't illegal, it's just that most corporate human resources departments avoid them because of potential legal liability.

There have been published court cases. No, I will not look up the references.