The ability to prevent certain employees from booking leave for the same dates

In our company, certain pairs/groups of employees are not allowed to take annual leave on the same day in order to ensure there is sufficient coverage. 

The "Clashes" tab can warn against this, but we would like a feature that allows us to define rules that will prevent the leave from being accepted if the rule is broken.

The rules could be for example:

1. If employee A is on leave, do not allow employee B to take leave
2. If Team A has three people on leave, do not allow a fourth person to submit leave