The state spy agency and police raided a number of locations linked to one of the nation's labor umbrella organizations on Wednesday on suspicions that some of its members violated the national security law.

From 9:10 a.m. on Wednesday, the National Intelligence Service(NIS) and the National Police Agency(NPA), engaged in a three-hour standoff with members of the Korean Confederation of Trade Unions(KCTU) at its headquarters in central Seoul before finally gaining access.

While the investigators arrived with a court-issued warrant on charges of violating the national security law, the labor group demanded that the search and seizure be conducted with its lawyers present, resulting in a scuffle between the two sides.

The NIS and NPA also raided the headquarters of the KCTU-affiliated Korean Health and Medical Workers' Union in southwestern Seoul as well as the residences of former executives of other KCTU-affiliated unions in South Jeolla Province.

According to the NIS, the raids follow a yearslong internal investigation into suspects alleged to have engaged in underground activities related to North Korea.

The investigation reportedly includes alleged National Security Act violations by some progressive labor figures on the southernmost Jeju Island.