A group of South Korean companies operating at a joint-venture factory park in North Korea has filed a formal complaint that the communist country's sudden decision to take a longer New Year's holiday seriously hurt their business, officials said Monday.

Currently, 123 South Korean firms are operating at the joint industrial park in the North's border city of Kaesong, producing garments and other labor-intensive products. Despite cross-border tension, the park has been running without any restrictions since 2004.

About 40,000 North Korean workers there had previously taken a one-day New Year holiday until this year when the North's authorities suddenly informed their Southern employers that the holiday was extended to three days.

On Monday, an association representing the South Korean companies delivered a formal protest letter to North Korean authorities over the decision, association officials said.

"The unexpected notice of the holiday for Jan. 1-3 caused major confusion to (South Korean) companies by hampering their normal production activities," the South Korean council said. "We very much regret (this move), and hope this will not occur again."

The council said due to the prolonged break, some South firms missed their production deadlines or had to pay wages twice the regular pay for North Korean workers who reported to work.

South Koreans celebrate the New Year's Day by taking off only one day. They instead takes off three days to mark the Lunar New Year's Day.

(Yonhap News)