The teams were told it was a mandatory event. However, it'd be hard for them to enforce a contract legally, when the teams were not aware in advance of what they were being asked to commit to (in terms of both the type of events, and the venues.)
I think it's not unfair to say that Notorious have put themselves on the wrong side of the Decorum rule a few times over the last couple of seasons, but any team deserves at least the right of reply before public announcements are made. I take it that the disciplinary committee has no formal appeals procedure in place?