The Korean Railway Workers' Union will go on an indefinite strike starting at 9 AM today.
This is their first indefinite strike in three years.
The decision comes as KORAIL workers and management again failed to reach a compromise on wages and employee numbers on Tuesday.
In preparation for the strike, KORAIL plans to send substitute workers to operate high-speed KTX and commuter trains.
But disruption to commuter services is still expected.
KTX bullet trains are expected to run at below 70 percent of usual levels, commuter trains 60 percent and freight trains to 30 percent.
During peak commuting hours on Wednesday morning, subways in Seoul will operate as usual --but during off-peak hours, they will run at about 80 percent of usual levels.