SEOUL - South Korean police began clamping down Monday on leaders of a railway strike which has halted 70 percent of freight train services and started taking a toll on industry.

Police said they summoned 44 union leaders for questioning on charges of leading an illegal walkout.

"If they ignore our summons we will seek court warrants to arrest them," a National Police Agency spokesman told AFP.

About 16,000 members of the 25,000-strong union of KORAIL, the country's railway monopoly, walked out Thursday in protest at the company's plans to cut jobs and wages and reduce welfare benefits to reduce its deficit.

KORAIL has filed complaints against 182 unionists for impeding business with an illegal strike.

Police say the strikers violated the law by stopping work to demand the reinstatement of dismissed workers.

President Lee Myung-Bak has urged stern action against the strikers, accusing them of hampering the country's efforts for economic recovery.

"There must not be a convenient compromise this time," Lee said Friday night.

"The walkout by unionised workers of public corporations, who are guaranteed lifetime job security, cannot be understood by the people at a time when hundreds of thousands of young people are struggling to land jobs."

KORAIL said the walkout had cost about 4.76 billion won (S$5.13 million) in losses as of Monday morning.

Some 70 percent of cargo train services remained idle Monday along with 40 percent of passenger train services.

KORAIL accounts for only about seven percent of the country's passenger and cargo transport but the strike has begun taking a toll on industrial activities.

Electronic firms and other exporters have not experienced any major problems but other companies which rely heavily on rail transport, such as cement and coal producers, have been hit hard.

"Our stocks have been increasing rapidly. If the current situation goes on, we have no choice but to keep our plants idle," Kang Byung-Chul, a Ssangyong Cement manager, told Yonhap news agency.

The walkout comes as Lee's administration is locked in tough negotiations over a bill seen by unionists as curbing their activities.

About 12,000 public-sector workers held an anti-government rally Saturday in Seoul after two umbrella union bodies threatened to stage a rare joint strike next month.

The bill would allow multiple unions at each workplace and ban employers from paying wages to full-time union officials.