Question regarding employees quitting with out notice.

We give our employees a monthly bonus based on the profit they make the
company for the previous month.

We have had a stipulation or policy that when a person resigns they must give us at least a two week notice in order to receive their last bonus check.

Are we within our right to require a two week notice in order for an
employee that is leaving to give us notice that they are leaving in order to
get their last bonus check?

To the best of my knowledge, you're fine with that policy.