Legal Question in Employment Law in California

Legal? Sure. And it is enforceable as long as it is part of the employment terms and policies you agreed to when you took the job. If this is a new policy being implemented for the first time, then you have the right to refuse, and seek a new job, or to accept the change. Many employers charge rent, such as apt building managers, etc. You are getting 'free rent' unless they charge for it. It should be 'reasonable' in amount. Remember, in general, unless you are civil service, in a union or have a written employment contract, you are an 'at will' employee that can be disciplined or fired any time for any reason, other than illegal discrimination under the Civil Rights, or Whistle-blower, or similar statutes. Your goal should be to keep your employer happy with you.