When they finally realize they need someone to fill the schedule all of a sudden, they'll be "asking"(really telling you) to work. In principle you should tell them to take a hike because you've made other commitments to fill the void that they created.

Accommodate them a 100 times with a smile and your a hero for the day. Deny them once and suddenly your being uncooperative. There comes a time when you must stand on principle, but be prepared for the back stabbing, kiss ass indulgences of incompetent management.

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Question Authority before it Questions you.