The Unification Ministry said Wednesday it has delivered a warning to dozens of firms at an inter-Korean industrial zone, as they violated its guidelines on wage hikes for workers there.

The ministry made clear that the companies will face punishment if they do not comply with the government's policy on the matter again, ministry spokesman Lim Byeong-cheol said.

The North is seeking to raise monthly wages for its 54,000 workers at the Gaeseong Industrial Complex by 5.18 percent to $74.

The South has rejected the communist neighbor's unilateral move, saying it is in breach of a 2004 agreement that calls for the two sides to set wages through consultations. The wage hike cap has been set at 5 percent per year.

The ministry immediately told the heads of the 124 South Korean firms there not to follow the communist neighbor's unilateral move.

But 49 of them were found to have paid increased March wages to their North Korean employees, apparently succumbing to the North's threats. Seoul first gave stern warnings to 18 firms and is now looking into the remaining violators.

"The government's probe into their motives is underway. We will take actions against companies that have not followed the government's guidance," the spokesman said at a press briefing.

In what could be a temporary relief, North Korea accepted South Korea's tentative offer in late May to pay wages at the current level, allowing the two sides to buy time for talks.

An official at the ministry said that the government plans to propose talks in the coming days, as the 10-day period of the wage payment for May will begin next Wednesday.

The wage row came as inter-Korean relations have been long strained since the North's torpedo attack on a South Korean warship and the shelling of a border island off the west coast in 2010.

The joint industrial park, which opened in 2004, is the last remaining symbol of inter-Korean reconciliation following a landmark inter-Korean summit in 2000. It has served as a revenue source for the communist country while South Korea has utilized cheap but skilled North Korean labor.

Meanwhile, Lim said that North Korea has not beefed up its control over movements at the industrial park due to concerns over the Middle East Respiratory Syndrome that has killed two South Koreans so far.

On Wednesday, South Korea confirmed five additional cases of the respiratory disease, raising the total number of those infected with the virus to 30.

Last year, the North imposed a travel ban on incoming foreign tourists for about five months due to concerns over the Ebola virus. (Yonhap)