Exact circumstance: Normal work schedule is 8:00-16:30, Mon-Fri. Altered work schedule would be for on-call work, shift from 11:30-20:00 Mon-Fri, once every 6-8 weeks. The purpose given is to lower overtime costs to the company.
I know it's a vague description, I can provide more details if needed.
I'm assuming there is no such law, however I have heard a few fellow employees mention they thought a law existed. The gray area is can an employer change your schedule for 7 days every few months and call it your new "normal work schedule"?

A link to the law or article number would be helpful if anyone knows the answer, allowed or prohibited.
JLaw