I want to add two Time Allowances for Time Card, one Non - Taxable and another Taxable.

I want to add two Time Allowances for Time Card, one Non - Taxable and another Taxable . User should be able to select Taxable Allowance only after he/she has selected non-taxable. Any help, I can get for adding this dependency b/w the two allowances.
Navigation: Login as en Employee -> Me -> Time & Absence -> Existing Time Cards -> Add -> Select Time Allowance