The 20,000-member Korean Railway Workers' Union launched an indefinite strike Thursday, calling for wage and bonus hikes.

This marks the first railway strike in 15 months, following one in September last year. The strike impacts Subway Line Nos. 1, 3 and 4, express KTX trains, and regular Saemaeul and Mugunghwa trains, all operated by Korea Railroad Corp.

It is reported that negotiations between the union and the railway operator on Wednesday ended without agreement. However, the union stated it remains open to resuming talks if the operator makes concessions.

Ahead of the strike, the union held rallies at major stations, including Seoul Station, Busan Station, Yeongju Station and Gwangju Songjeong Station, as well as outside the Korea National Railway headquarters in Daejeon.

In response, Korail has implemented an emergency transport plan, deploying 14,861 personnel -- 10,348 essential staff and 4,513 substitutes -- covering 60.2 percent of its usual workforce.

During the strike, subway operations are expected to run at 75 percent for general hours and at over 90 percent during rush hours. KTX trains will run at 67 percent, and Saemaeul and Mugunghwa trains at 58 percent and 62 percent, respectively.

Korail said it will enhance passenger notifications through its mobile app, website, station announcements and onboard displays. Real-time updates on train schedules will be provided via app and website pop-ups, as well as text message alerts.

During the strike, ticket cancellation and change fees will be waived, with full refunds automatically issued for canceled trains.