A local city mayor has alleged that an agent of the National Intelligence Service has until recently conducted illegal surveillance on him and meddled in the local elections slated for June.

The allegations, raised by Lee Jae-myung, mayor of Seongnam City just outside Seoul, add fuel to the row over the state spy agency’s alleged involvement in politics.

In a news conference Tuesday, Lee claimed that an NIS agent covering the city has until recently collected negative information about him in a bid to influence public opinion in the run-up to the mayoral election.

Specifically, Lee claimed that the NIS intelligence officer met with the vice president of Gachon University on Dec. 30 to discuss the controversy surrounding the mayor’s master’s thesis, which was suspected of having been plagiarized.

Suspicions that Lee might have committed plagiarism were first raised in September by three potential mayoral candidates of the ruling Saenuri Party. Lee, a member of the main opposition Democratic Party, surrendered his master’s degree to avoid controversy.

Lee said the NIS officer had explained the controversy over his thesis to the university official, who had no knowledge of it. Furthermore, he demanded that he be given a copy of the controversial paper.

The mayor asserted that the NIS agent had breached the law on the spy agency by collecting and distributing information that had nothing to do with his job, abusing his official authority, and intervening in politics.

Lee also alleged that the NIS officer collected information about the promotion of a city government official in November in another case of explicit abuse of authority.

Flatly denying these and other allegations raised by the mayor, the spy agency said it would sue him for libel and claim damages.

The court will decide who is telling the truth. But Lee’s allegations suggest that NIS agents have until recently continued to make routine visits to public and private institutions to collect intelligence, a practice that has become illegal following the passage of the NIS reform bills in the early hours of New Year’s Day.

Lee’s allegations could trigger a political storm, as the DP is moving to investigate them. It is planning to launch a nationwide campaign to encourage citizens and public officials to report illegal activities by NIS agents, including meddling in local elections.

If tips about illegal NIS activities come in, they will back up the party’s call for the appointment of a special counsel to investigate the spy agency’s alleged meddling in the 2012 presidential election.