Police on Thursday arrested the head of the Korean Confederation of Trade Unions for organizing a rally in Seoul in defiance of COVID-19 rules.

Officials from the Seoul Metropolitan Police Agency on early Thursday morning arrested Yang Kyung-soo, head of the KCTU, at the labor group’s office in Jung-gu, central Seoul. Dozens of officers were dispatched to the scene for the arrest, which took around 40 minutes.

Some KCTU members attempted to block police when they entered the building, but no major physical clashes were reported while officers were executing the warrant. Yang was brought to Seoul Jongno Police Station.

The arrest comes 20 days after a local court issued an arrest warrant for Yang who organized a rally of 4,701 people on July 3 in violation of Level 4 social distancing rules.

The warrant was issued for Yang ahead of a major KCTU rally scheduled for Oct. 20, in which 1 million participants are expected to attend. Yang has argued that the arrest warrant is unjust, citing the right to assembly and freedom of speech.

Yang and other KCTU members have stayed inside the union’s office to avoid being detained. Police had to obtain additional warrants to enter the premises for the arrest.

A handcuffed Yang, before stepping into the police vehicle, urged other KCTU members to continue preparing for the October rally. The collective action was needed to reinstate laborers’ demands and fight unjust measures coming from the Moon Jae-in administration, he said.

After Yang’s arrest, the KCTU said in a statement it would “take revenge on the declaration of war” from the Moon administration with a “strong full-scale strike.”

The labor group denounced the actions on Yang as a “mistaken decision” from the ruling administration, which would only serve to further infuriate laborers. It also warned that no administration ended well after waging conflict with laborers.