If you are required to answer, you are on duty per the Whitlow letter. You'd better check the legality of that.
It hasn't been implemented for pilots yet. The F/A's have it in their CBA. It was part of that insulting offer they company put out. You're right, I don't see how it could possibly be legal. Little things like legality rarely stand in the way of some of the boneheaded decisions made around here.