The police have raided three locations linked to a construction workers’ union under one of the major umbrella groups over allegations of coercion in hiring and on-site demands for money and valuables.

The Seoul Metropolitan Police Agency on Tuesday searched the northern capital area headquarters of the union under the Korean Confederation of Trade Unions(KCTU) in Seoul's Mapo District as well as the homes of two officials.

The police are looking into whether officials at the union's regional headquarters were also involved in the alleged illegalities.

Earlier, investigators raided the union's office representing southwestern Seoul and sought arrest warrants for three executive-level officials working on site.

The three officials are suspected of blackmail and coercion in violation of the Law on Punishment of Violent Acts. The Seoul Central District Court is set to decide on the warrants later on Tuesday.