Concerns over possible nationwide rail disruption grew as unionized workers announced Thursday that they would go on an indefinite general strike on Dec. 5 to demand a wage increase and a bigger workforce.

If implemented, the strike is expected to affect the operations of high-speed KTX and other regular train services nationwide, as well as subway services in the capital area, including the operation of Subway Line Nos. 1, 3 and 4 and the Suin-Bundang line.

The Korean Railway Workers' Union, representing unionized workers at the state-run Korea Railroad Corp., also known as Korail, has been staging a slowdown, or work-to-rule protest — in which workers pledge to only do the contractual bare minimum — since Monday.

The union said in front of Seoul Station that its members will launch an indefinite full-scale walkout starting Dec. 5 if there is no change in the attitudes of the government and their employer, Korea Railroad Corp., which could be the first such strike since September last year.

"The general strike will be an inevitable choice. The struggle of railway workers to ensure the safety of citizens and trains and the recognition of their fair labor is justified," the union said.

The unionized workers continue to demand a base salary increase of 2.5 percent, hiring additional personnel to address severe understaffing, and transitioning to a four-team, two-shift work system to prevent consecutive night shifts. They are also advocating for a fair promotion system.

The union said in a press release that the Finance Ministry is pushing to cut the number of Korail employees by 1,566 positions despite ongoing staff shortages, which would worsen workloads, conditions, and safety for both workers and passengers. The national railway operator, however, said it has "no plans yet" to downsize.

The planned walkout is expected to cause widespread rail service disruptions nationwide, as the labor union representing Seoul Metro workers — responsible for operating subway Line Nos. 1 through 8 — has already announced a full-scale strike set for Dec. 6. These subway workers began a work-to-rule protest on Wednesday, adhering strictly to their stipulated duties and refusing any additional tasks. The union demands wage increases and additional staff hires. If their demands are unmet, the general strike will proceed as scheduled.