An opposition South Korean lawmaker issued a warning against “election interference” after the Chinese ambassador to Seoul criticized local presidential candidate Yoon Seok-youl.

Park Jin, 64, said Friday in a Facebook post that Ambassador Xing Haiming had “shown disrespect for diplomatic customs” after making “very regrettable” remarks about Yoon, Dong-A Ilbo reported.

Park said Xing’s remarks challenging a “prominent presidential candidate on foreign policy and national security” are a “clear violation of sovereignty.”

Park’s statement comes after Xing wrote an opinion piece published to South Korea’s JoongAng Ilbo on Friday.

Xing said in his article that the U.S.-South Korea alliance “must not harm China’s interests” and that the alliance should not dictate China-South Korea ties.

Xing’s piece was a response to a JoongAng interview with Yoon published Thursday. The South Korean presidential candidate had said that the U.S.-Korea alliance is the “solid foundation” on which to “strengthen cooperative relations with countries that share our values.”

South Korea can only conduct diplomacy with China within this framework, Yoon had said, while defending Seoul’s decision to deploy the U.S. missile defense system THAAD in 2016, a move that upset Beijing.

“If [China] wants to insist on THAAD withdrawal, it must first withdraw its long-range radar deployed near its borders,” Yoon had said.

Xing claimed in his article that South Korea’s decision to deploy THAAD “seriously undermined China’s security interests” and the people of China have felt “less safe” since the decision.

Choi Kang, vice president of the Asan Institute for Policy Studies, said that Xing’s article “could be misinterpreted as being disrespectful while regarding Korea as an easy opponent,” the Chosun Ilbo reported Friday.

It also is not common for an ambassador to comment on a host country’s domestic candidates. China’s central government could have “pressured” Xing to write the piece, Choi said.

China imposed informal sanctions against Korea after Seoul decided to move forward with THAAD deployment. Seoul has avoided confronting Beijing on its human rights record and ongoing crackdowns in Hong Kong and Xinjiang.