Can an employer cancel vacation approval they gave many months ago because a project is not done ? Is taking the vacation grounds for dismissal ?

Thank you for the question. It is unlikely an employer can force an employee to cancel a vacation planned and approved months in advance. It's also not likely grounds for dismissal. I'd encourage you to give us your call at the number below to discuss your situation in more detail. In these kinds of situations, you certainly want legal advice from an experienced employment lawyer before making any kind of decision.