Isn't this a violation of the Labor Standards Act?

The situation you described is highly likely to constitute a case of violation of the Labor Standards Act.

First, if the employer has failed to pay an additional 50% or more of the ordinary wage for extended, night, or holiday work, it has violated the obligation under Article 56 (Extended, Night, and Holiday Work) of the 「Labor Standards Act」.

In addition, the act of not paying severance pay is also a violation of Article 36 (Duty to Settle Money and Valuables) and Article 43 (Principle of Wage Payment) of the same Act, and if a worker does not receive wages or severance pay within 14 days after leaving employment without justifiable reason, the employer may be subject to criminal punishment.

In this case, the worker can file a petition with the competent local labor office.

A petition can be filed in person or online through the Ministry of Employment and Labor website.

If you submit documents that can prove the fact of employment and of the arrears or nonpayment, such as the employment contract, pay statements, attendance records, and bank deposit records, the labor inspector will request the employer to appear, confirm the facts, and issue a corrective order or take measures to book the case as a criminal matter.

An employer that violates the Labor Standards Act may be subject to imprisonment for up to three years or a fine not exceeding 30 million won (Article 109), and if the amount of unpaid wages is large or the conduct is repeated, the employer may also be subject to a detention investigation by the labor inspector.

In addition to a petition, a worker can also claim unpaid wages through civil procedures (a payment order, a civil lawsuit, or provisional attachment), so you may wish to take the necessary legal steps.