Seven lawmakers from the main opposition Democratic Party of Korea flew to China on Wednesday for talks with Chinese government officials and scholars over the planned deployment of an advanced American missile defense system on the Korean Peninsula.

Their visit comes amid apparent Chinese retaliation against South Korea for its agreement in July last year to host the Terminal High Altitude Area Defense system. China recently refused three South Korean air carriers’ applications for nonscheduled flights for this month.

The disapproval is a lost opportunity for the air carriers, which had expected a surge in bookings in line with the Lunar New Year holiday later this month.

Beijing has not allowed a single K-pop artist to perform in China, one of the biggest markets for Hallyu, since October last year. It reportedly even told Chinese broadcasters to take Korean dramas, movies and entertainment shows off the air.

China also excluded cars equipped with Korean-made batteries from a list of electric cars eligible for state subsidies.

Beijing seems to have allowed the lawmakers’ visi, as they reportedly will deliver messages from Moon Jae-in, a strong contender in this year’s presidential election, who has called for a reconsideration of the THAAD deployment.

Beijing’s response toward the lawmakers presents a marked contrast to China’s attitude toward South Korean Ambassador to China Kim Jang-soo, whose requests for meetings with senior Chinese officials have been snubbed since the THAAD agreement.

China should stop such retaliatory measures.

THAAD is a purely defensive system for South Korea, which must defend itself from North Korea’s nuclear and missile provocations. Its deployment is entirely a security and military matter, which has little to do with culture and the economy. The right way to solve the THAAD issue should be dialogue through related official channels, not via unofficial contact with anti-THAAD figures.

It is little surprise that policy changes happen through negotiations between two sovereign states. Military policies, however, are different from other policies. Most of them are directly linked to the survival of a nation. A sovereign state will not change its bedrock policies just because of external pressure and without going through proper procedure.

Beijing claims the US missile defense system, if deployed on the Korean Peninsula, would threaten its interests and the regional security balance. It argues its real aim is to deter weapons systems not only in North Korea but also in China’s hinterlands.

If China wants to stop the THAAD deployment, it needs to rethink its North Korea policy and understand why South Korea decided to deploy the system. Pyongyang’s nuclear project threatens all countries including China. Each time North Korea has conducted nuclear and missile tests, the international community has toughened sanctions on the regime. China has joined the international community in sanctioning the North, albeit somewhat reluctantly.

In his New Year’s address, North Korean dictator Kim Jong-un vowed to strengthen the country’s nuclear pre-emptive capability and enter the final stage of test firing the intercontinental ballistic missile.

If China, South Korea and the international community presses Pyongyang to abandon its nuclear ambitions, and Kim succumbs to the pressure and sanctions, the rationale for the THAAD deployment on the Korean Peninsula will disappear.

Regarding the lawmakers’ visit to China, they should act prudently. They reportedly plan to raise the issue of China’s economic and cultural retaliation against South Korea. It is the appropriate thing to do. However, considering the current political situation, their visit may not reap the desired outcome of easing tension, but might instead deepen division and conflicts in South Korea over the THAAD issue.