According to Article 37 of the Labor Contract Law: "The employee may terminate the labor contract by giving a written notice to the employer 30 days in advance. The employee may terminate the labor contract by notifying the employer three days in advance during the probation period. " It is legal for workers to resign according to this regulation, and it does not need the approval of the employer. They can leave their jobs then.
If the employer deducts wages for this reason, the laborer can apply to the Labor Arbitration Committee for labor arbitration (free of charge) and get his wages back.