SEOUL, Dec. 22 (Yonhap) -- More than 100 striking railway workers were taken into custody Sunday after the police forced their way into a union office with tear gas to round them up for questioning.

Some 600 police officers were deployed to raid the headquarters of a militant labor umbrella group, the Korean Confederation of Trade Unions (KCTU), in central Seoul around 11 a.m. to arrest union leaders of the state-run Korea Railroad Corp. (KORAIL) who have been defying summons by prosecutors.

The unionists fought back with water cannons as riot police forced their way in with tear gas.

The tense standoff lasted for more than two hours before the police whisked away 131 KCTU members.

In protest at the police raid, the KCTU said its key members will begin an indefinite strike on Monday and a general strike on Saturday.

"The government's raid of the KCTU office and oppression of rail workers is a declaration of war against all of the nation's workers and democratic unions," Kim Gyeong-ja, deputy head of the union, told reporters after an emergency leadership meeting. "We will show our anger toward the heart of the regime by staging a general strike on Saturday."

More than 6,500 unionized KORAIL workers walked off the job two weeks ago in protest against a government decision to set up a KORAIL subsidiary to run part of the high-speed train services. The union suspects the move is a scheme to privatize KORAIL, leading to mass layoffs. The government said the strike is illegal.

Shortly after the raid, the government renewed its ultimatum to the union and ordered the striking members to return to work.

"It has come to a point where the government cannot tolerate this any longer, as the prolonged illegal strike has resulted in inconvenience to the people and losses to the national economy," Transport Minister Suh Seoung-hwan said.

The minister also urged union members to comply with arrest warrants.

Last week, district courts across the country issued warrants to arrest 25 strike leaders, including the union head Kim Myung-hwan, after they repeatedly refused to appear for questioning.

The government says that the subsidiary's establishment has nothing to do with privatization, and that the new unit will be owned by KORAIL and state-run investors. In a move to convince the workers, the government also said it will issue a license for the new affiliate to operate only on the condition that its stake never be sold to private investors.

On Sunday, the rail union refuted the government's claim, insisting it is nothing but "a shallow ploy to deceive the people."

"Privatization of public firms has so far begun with turning them into corporations, a method which is being pushed by the government now," the union said in a statement.

The new service by the affiliate is scheduled to run from Suseo-dong in southern Seoul to the southeastern port city of Busan from 2016.

Opposition lawmakers moved quickly to protest the police's raid on striking unionists.

The main opposition Democratic Party (DP) convened an emergency meeting of party leadership to discuss how to respond to the government's actions while five of its lawmakers made protest visits to the police headquarters.

The party also decided to demand three related parliamentary committees open their sessions on Monday with a plan to rebuke the government for the raid and demand the peaceful settlement of the dispute.

KCTU and civic groups instantly issued a series of statements denouncing the government's use of force.

"The government's act of raiding the office of KCTU, the symbol and the heart of the democratic trade union movement, is tantamount to an attempt to annihilate the labor movement and create a dictatorship to trample down the just demands of workers," said Shin Seung-cheol, chairman of the KCTU, in a statement posted on his Twitter account.

The People's Solidarity for Participatory Democracy, a leading civic group in Seoul, criticized the government and the state-run rail operator for "trying to resolve the crisis with the use of force, ignoring civil society and the labor circle's raised questions on the impact of privatizing the national rail service."

It said the government damaged the integrity of the plan and the public's confidence in it by opting to haul the unionists in for questioning.