Can my Boss do this??

[A S U]

So for the last 4 years i've been working at this company. Schedule for all full-time employees has been Mon-Fri, fluctuated from 8-5 to 7:30-4:30. We are moving offices at the end of the month. My Boss is telling everyone that office is closed that Friday and we will work that Saturday to set up desk make sure we are 100% operational for Monday. So can my boss do this? I'm an hourly employee in CA. I've looked up California labor codes, but can't find anything, plus it's like 1500 pages long. Our employee manual does state office hours. Naturally I have plans that weekend, plus i'm a little ticked that I have to give up my weekend cause my boss is too cheap to pay extra for moving on a saturday.

Also feel free to add when a boss has tried to screw you.