Set Up maximum limit for a vacation

Dears,

I need to create a vacation type and then set a maximum limit of hours for this vacation during the calendar year. What i did is that i created a pay type for this vacation type and then i created an accrual because based on the this accrual i calculate some deduction. What i need to do is to find a way that when trying to enter the pay type of this leave with a number of hours more then the annual permitted the system stop the user from entering it.

Ex. 1: If the annual limit is 150 Hours and the taken leave hours during the year is 50 Hours, so i need that when trying to enter a leave for more than 100 Hours the system prevent the user from entering it.