Put it on the sign out front: "We fire our workers every six years whether they deserve it or not".

We know they won't, because the policy is designed only to lock workers into low wages. Since most casino gamblers are hourly workers wasting their money on vacation they'll be able to relate this happening to them at their job.

No one this side of a corporate boardroom can say this is a good idea, and I hope local unions make this policy clear to people considering a place to gamble. They aren't the only place in town waiting to steal our money.

on edit:
How do they even get away with this? Isn't this what the airlines tried to do decades ago to ensure young attractive stewardesses? Next the company will have a physical test where female workers have to fit under a desk.