Legal Question in Employment Law in California

No. That violates Labor Code Section 224. If the employer can show that the shortage was the result of gross negligence or willful conduct, a deduction MAY be allowed, but likely it will not be allowed. It is hard to see how the employer could punish a group of employees, unless the employer has some good evidence that the group of employees stole from the register or intentionally left it open for others to steal from.

No, but they can fire everyone involved. IF they could prove someone stole, then they can collect that money from that person[s] by suing, and could file criminal charges for theft..