Let him know that the next memo would lead to questions on his continuation with the company.(kindly discuss the same with your manager / head). In this perod of recession - he needs to play safe.
always remember WHATEVER GOES ALWAYS COMES AROUND
Taking leave is not a big issue until the employes gives prior intimation. An employer in no way can restrict him from his eligible leave. also you have to justify and analyse his leave case to case based on the reason of his / her leave. Also check whether an employee is a habitual absentee in nature, his past reasonwise leave history and all that. Then issue a warning memo as per companies standing order.
hope this will give you a clear picture to you