That sucks I am glad you are going to get good references from the one supervisor. A consultation with a lawyer doesn't hurt, but this may be one of those incidents where you are better off just putting it behind you. If he is in his 70s, he may retire in a couple of years. If you continue friendly relations with the supervisor, maybe you could go back to that company then?

It makes you wonder, though - if he has been there, doing this for 20 years, it doesn't speak very well of the management.