As long as the unit arranges workers to work no more than 8 hours a day and 44 hours a week in accordance with the relevant provisions of the Labor Law, it should not be considered illegal.
Because China's "Labor Law" stipulates that the purpose of statutory working hours and statutory holidays is to protect workers' right to rest, but three shifts have not deprived workers of their right to rest.
Where an employer arranges employees to work on legal holidays such as May Day, November Day, New Year's Day and Spring Festival, whether they rest or not, they shall be counted as overtime work on holidays. In accordance with the provisions of the Labor Law and the Labor Contract Law, overtime pay shall be calculated according to the standard of three times the salary.