Legal Question in Business Law in California

I'd say "yes" if the policy or the right to "dock" is made clear in advance, e.g., by being set forth in an employee handbook or some similar means. The right to "dock" is otherwise less certain, and if it is just an after-the-fact punishment, it's probably illegal. The general principle is that, with few exceptions, the employer can make its own rules, but must make them beforehand and communicate them to the employee, and cannot make up and enforce punitive rules retroactively.

Only 'salaried exempt' employees are immune from time deduction / docking. Read your company manual to see what the policy statement is. If you seriously believe they are not allowed to do so, you can file a claim with the Labor Commissioner, whose decision will be the 'last word' on it.