SEOUL - South Korea's pro-business government on Tuesday sent in police to raid the offices of striking railway workers, refusing to negotiate over what it calls an illegal walkout.

State-run Korail broke off talks with the union last week, calling its demands for a pay hike and reinstatement of fired members unreasonable.

It has been using non-union workers and military engineers to try to keep services running during the six-day strike.

"We will not compromise," Labour Minister Yim Tae-hee told a joint news conference with the Finance, Transport and Commerce ministers.

"This is an illegal and unjust strike called at the expense of the national economy and public order."

The refusal to resume negotiations by management reflects the hard line against militant unions by conservative President Lee Myung-bak, who has pledged to end years of disruptive labour action he says is undermining South Korea's competitiveness.

In August, riot police were used to crush a strike at embattled Ssangyong Motor Co over a massive layoff plan.

In the end, union leaders had to drop their key demands.

Passenger train services and part of the Seoul subway system run by Korail were operating at near normal capacity although delays were reported.

Cargo transport was down sharply, however, operating at a third of normal volume.

The commerce minister and the customs commissioner said at the news conference that the alternative of moving cargo by trucks was not cost effective and could impact the country's efforts to pull out of a global downturn.

Korail chief executive Huh Joon-young, a former national police chief, said management was not going to give in to "unreasonable" union practices.

"We're going to make sure we teach the union a lesson this time," he said in an interview with a local daily.

Organised labour, long a dominant and disruptive force in South Korean industry, is already bending under the impact of the economic downturn, a conservative government set on curbing what it considers investor-scaring ways, and scandals and mass defections at the Korea Confederation of Trade Unions (KCTU), a major labour federation.

The government is trying to push through legislation that will end the practice of companies having to pay union leaders, allow multiple unions in a single workplace and double to four years the period that firms can employ contract - and usually non-union - workers.