Job (private school in NY) is randomly telling us that it’s mandatory to come in to work 2 days during our summer break to set up classrooms – wtf

The school calendar, which is on their website, clearly states that school is closed during the August break, and that teachers have 2 days that we are scheduled to come in during the beginning of Sept before students return the following week.

Now they are randomly making this demand to give them 2 more days. Is this allowed? Would employees face repercussions?