Legal Question in Employment Law in California

Of course.

Only if you want to keep your job. Employers are free to fire employees for any reason, or even no reason at all, as long as it is not for reasons of discrimination on the basis of a protected classification (such as race, or gender), is not in violation of anti-retaliation laws (such as for union organizing or whistle blowers), and not in violation of a union or private contract, or civil service rules. So if they want to fire or discipline you for violations of employee rules while off work, they are completely free to do so.

On company property, of course.

In general, unless an employee is civil service, in a union, or has a written employment contract, they are an 'at will' employee that can be disciplined or fired any time for any reason, with or without �cause�, explanation or notice. Any employee's goal should be to keep their supervisors happy and make them look good to the company, and make the company money. That�s how the company pays employee wages. If you don't, then don't be surprised to be replaced.