Legal Question in Employment Law in California

I'm afraid so. Unless you have a signed contract guarantying certain hours, your employer is not obligated to give you any hours that they don't want or need you to work.

The only theory that I can think of that might help you is that you might be being discriminated against because of your religion. I am *not* saying that discrimination is occurring -- merely that it is conceivable. If your employer has a legitimate need for an employee on Sundays, and would have taken the same action with respect to you regardless of your reason, then unlawful discrimination does not exist and you would not have a claim.

You should speak with an employee-side labor lawyer for advice and guidance.