illegal.

1. According to the labor law and social insurance law of China, employers are obliged to buy social insurance for their employees, including endowment insurance, medical insurance, work injury insurance, unemployment insurance and maternity insurance. Employers must pay social insurance premiums in accordance with the statutory proportion, and deduct the employee's personal social security contributions from his salary.

2. Social insurance is the legitimate rights and interests of employees. It can provide employees with pension, medical care, work injury and other protection, and employees can enjoy corresponding welfare benefits after leaving their jobs. If restaurants do not pay social security to employees, it will deprive employees of the opportunity to enjoy these rights and interests, which violates the principle of protecting employees' rights and interests. Therefore, it is illegal for restaurants not to pay social security to employees.