There are a couple of ways you *could* go about it.
1) go to the supervisor overseeing the production and bring up the 6 day work week contained in the manual. remind them that productions are only supposed to rehearse 6 days a week and that the day off is not only an industry standard, but also necessary to keep cast and crew refreshed and focused.
2) When scheduling rehearsals with the director, bring the 6 days up to them. And don't schedule on the 7th day.
3) Take a formal/informal poll among your Peers regarding the 6 day work week in the handbook. If they feel like making a thing out of it, write a formal letter of complaint to the department reminding them of their own guidelines and asking that the 6 day work week be enforced, with the student body as the undersigned.
Those are just a few ways to go about it. Don't be confrontational about it per se. Even if you elect to go with option 3, be very formal and not adversarial at all. Stick to facts.