A. The defendant is a hospital established and operated by Seoul Special Metropolitan City pursuant to the Seoul Special Metropolitan City Ordinance on the Establishment and Operation of the Seoul Special Metropolitan City Hospital in order to provide medical treatment to older persons and community residents and provide health and medical services to older persons, and the plaintiffs are employees, such as nurses belonging to the defendant.

Seoul Medical Center (hereinafter referred to as the "Seoul Medical Center") has been entrusted by the defendant since the opening of the defendant around May 2006 in accordance with the Agreement on the Operation and Management of Seoul Medical Center on October 26, 2015 with Seoul Special Metropolitan City.

B. The defendant's rules of employment and [Employment Rules] Article 25 (Use of Annual Leave and Compensation) (5) Where an employee does not use annual paid leave, he/she shall pay annual paid leave allowances as prescribed by the remuneration regulations.

Article 38 (Overtime Work, Night Work, Holiday Work) (1) An employee shall, if necessary for hospital work, perform overtime work, night work, or holiday work.

(2) Allowances shall be paid to employees who have worked pursuant to the provisions of paragraph (1) as prescribed by the remuneration regulations.

(3) Night work shall be between 22 p.m. and 6 a.m. on the following day.

Article 48 (Remuneration) Remuneration regulations shall govern the provisions of remuneration regulations for employees.

[Remuneration Provisions] Article 3 (Definition of Terms) of the General Provisions of Chapter 1 (Definition of Terms) is defined as follows:

1. The term "annual salary" means the total amount of wages determined on a yearly basis and received by the relevant employee during the period of an annual salary contract, excluding the wages outside the annual salary;

2. The term "basic annual salary" means a constituent element of an annual salary, of a basic nature corresponding to each class to which an annual salary is applied, which is an amount calculated by multiplying 54% of the annual salary by the applicable rate of 54%;

3. The term "non-annual salary" means a pay of a personal nature, including annual allowance, overtime work, day-day work, and night work allowance;