I keyed in a few terms and did find this. Although it rests on a withdrawal of a job offer, "Promissory estoppel" "may" have some bearing in your case?
It seems there may be an "implied" promise not to terminate you for doing something he approved, ergo he was "estopped" (stopped) from the action he took.
An employment law attorney would need to be consulted.
Rest assured though, he will lie about permission being granted IF the law supports YOU.

