It's certainly no rumour. Text just sent round by BASSA:
According to this forum, Bassa did sent some texts out claiming that almost no one did turn up to work. Or that planes are departing with no luggage loaded. That and more turned out to be incorrect. Therefore I believe that this is just another fabricationby Bassa to stop crew from coming to work.
Also, I'm working in Europe House and have not heared anything about a no-strike-pledge being drafted. And I have many eyes and ears