North Korea has notified South Korea of its unilateral decision to raise the minimum wage for its workers at the Kaesong Industrial Complex by 5.18 percent, the unification ministry said Thursday.

In a fax message sent Tuesday, the North said it would increase the minimum wage from $70.35 to $74 starting on March 1, a ministry official told reporters.

In addition, the North announced that it would collect 15 percent of their basic wage plus overtime payments as "social security," he said. Currently, the South's firms pay 15 percent of the basic wage alone.

The North Korean workers' average wage amounted to $141.4 per month in 2014, according to the ministry's data.

Under Pyongyang's plan, South Korean firms will have to pay $164 on average for a North Korean worker a month, up 5.53 percent from the current $155, said the official.

He stressed that the South's government can't accept the North's move.

"The two sides are supposed to set wages for workers at the complex and other working conditions through mutual consultations," he said.

"The government will advise our firms to pay the current level of wages until the issue is settled through consultations between the related authorities of the two sides."

Those companies are scheduled to pay March wages for the North's workers between April 10-20.

Earlier Thursday, the South attempted to deliver a protest letter, but the North refused to receive it, said the official.

"It's very regrettable that the North shows such an attitude," he said.

About 120 South Korean garment and other labor-intensive plants employ more than 53,000 North Koreans at the complex, which was created in 2004. (Yonhap)