We paid a worker in advance for a vacation he never took–what are our options?

Q: “My client’s employee requested accrued vacation leave and was paid for the weeks in advance of the vacation. Then he changed his mind on the Monday of his vacation and came to work for the entire paid vacation. How do we handle his paycheck for the workweeks? Can we deduct the vacation pay from his workweek pay (making sure he doesn’t go below minimum wage)? If not, how can we get reimbursed for the vacation pay? I intend to add a statement to the vacation policy that prohibits employees from working on their approved vacation.” – Ken, New York