Section 24 of the EA says deduction can be done if it is overpayment by mistake. But in your case, it is giving more leave than he is entitled to. I am not sure whether you can grab his balance of salary to pay for it. Consult the Labour Department for proper advice.
24. Lawful deductions.
(1). No deductions shall be made by an employer from the wages of an employee otherwise than in accordance with this Act.
(2) It shall be lawful for an employer to make the following deductions:
(a)deductions to the extent of any overpayment of wages made during the immediately preceding three months from the month in which deductions are to be made, by the employer to the employee by the employer's mistake;