I'll weigh in. I don't know of any previously approved VACATION being cancelled. That is time covered by accrued vacation time.

I do know of previously approved UNPAID TIME OFF being revoked. And that is specifically covered in the section of the handbook that talks about the approval of such time. If scheduling requires it, such as for sick calls and resignations, then the pilot can be called back in. In such a case they are paid time and a half for the days they would have originally been off.

I also know of vacation that isn't approved or disapproved until last minute because of the staffing issues we have been having. But that is just so we DON'T have a situation of a pilot being told "Yes, your vacation is approved" and then have to cancel it because that is the only way to staff a run.