North Korea is blocking South Korean workers' access to a jointly run factory park in the north.
Some 860 South Koreans work in the the Kaesong industrial complex. The factory park started producing goods in 2004 and has been a point of cooperation between the North and South.
"They were working normally when I called them in the morning," said Park Yun-kyu, head of a men's apparel maker in Kaesong.
"The problem is food," he continued. "I hope North Korea would at least let us send food. We have to send food and some materials for production every day."
Pyongyang's decision to refuse the workers follows its repeated threats to stage nuclear and missile strikes on Seoul and the United States.
Lee Choon-kun, a North Korea researcher at the Korea Economic Research Institute, a Seoul-based think tank, called the move a "slap in the face."
"I see this as a start for more provocative actions," he said.
North Korea is threatening to shut the factory down, which produced $470 million worth of goods last year.