A nationwide strike by unionized railway workers set to begin Tuesday is expected to significantly disrupt train operations, with subway services projected to run at 25 percent below normal levels.

The Korea Railroad Corporation(KORAIL) said Monday that subway lines it operates, including those in the capital region and regional routes in Gyeongsang Province, will run at about 75 percent capacity during the walkout.

Although the legally mandated minimum service level during a strike is 63 percent, KORAIL said it plans to maintain roughly 75‑point‑four percent of normal subway operations by deploying substitute workers and military personnel.

The company warned, however, that train intervals on some routes could stretch to between 40 minutes and one hour if the strike proceeds as planned.

KORAIL said high‑speed rail services will operate at 66‑point‑nine percent of normal levels, capital‑area subways at 75‑point‑four percent and regular trains at 62‑point‑four percent, raising concerns about heavy congestion during the year‑end travel season.

The Korean Railway Workers’ Union plans to launch the strike at 9 a.m. Tuesday, with about 12‑thousand members expected to participate. The union is also planning a large rally at 2 p.m. in Seoul’s Gwanghwamun area, demanding that performance‑bonus payments be raised to 100 percent of base pay from the current 80 percent.