Seoul says North Korea is refusing to allow South Korean workers to enter a jointly-run factory park just across the border in North Korea.
Seoul's Unification Ministry says about 480 South Koreans planned to travel to the park in Kaesong on Wednesday. Spokesman Kim Hyung-suk says Pyongyang is allowing South Koreans to return home from Kaesong but not enter.
Hostility between the neighbors is high following weeks of threats after North Korea conducted its third nuclear test.
Pyongyang threatened last week to shut down the park. It's the last remaining symbol of detente between the rivals.
The Korean Peninsula is technically in a state of war because the Korean War ended in a truce.