Korea's railway union members started an indefinite walkout around three hours ago.
The union is strongly opposed to the transport ministry and KORAIL's plan to form a subsidiary to manage new KTX routes departing from southern Seoul.
Labor workers argue the government's move will eventually lead to the privatization of KORAIL.
The negotiations between union workers and management lasted well into Sunday night -- but the two sides failed to find middle ground.
Railway officials say commuters in Seoul and the metropolitan area should not be affected as KTX trains and Seoul's subway lines will operate normally.
Operations of regular train services such as Saemaeul and Mugunghwa will drop to 60 percent, and freighter train services will drop to around a third of normal levels.