Legal Question in Employment Law in California

No, it is not legal. If your employer believes that you made an error or stole money, your employer can fire you and/or sue you for the money. Your employer may not help himself/herself to deductions from your check unless you agree to it in writing.

No. You are entitled to full pay, regardless of drawer shortage, unless he can prove theft or gross negligence by you, not simple mistake or negligence. Your remedy is to demand full payment of all those withheld amounts, and if denied that, then you can bring a legal claim at the local Labor Commissioner or a civil lawsuit for unpaid amounts, interest and penalties. Then if you get fired for making your claim, you may have a separate legal action for 'illegal' wrongful termination. If that happens, feel free to contact me. I'll be happy to represent you in both those matters. I've been doing such employee rights matters for many years.