The Korean Confederation of Trade Unions members call on Yoon to step down in a rally held May 17 in central Seoul. (Yonhap)

The ruling People Power Party said Monday it may consider taking legislative action against the country’s main umbrella labor union, with four of its leaders recently indicted for alleged anti-government activities in collusion with North Korea.

In the indictment released Friday, Seoul prosecutors said four of the Korean Confederation of Trade Unions members holding leadership positions communicated with North Korean authorities on at least 90 different occasions in the planning and execution of several protests against the Yoon Suk Yeol government over the past year.

Prosecutors found that some of the protests led by the union confederation, after secret communication with North Korea, include ones calling for a halt to South Korea-US joint military drills.

Speaking at a meeting of party leadership on Monday, ruling People Power Party chief Rep. Kim Gi-hyeon accused the umbrella union of being “invested in promoting anti-government” causes rather than representing workers’ interests, citing the indictment.

He added that his party may be preparing legislation to restrict protest activities late at night from taking place, calling an all-night protest held last week illegal.

The union confederation, which is a fixture at major protests against Yoon and his conservative administration, was among those participating in the latest anti-Yoon rally that took place in Seoul on Saturday, in time for the G-7 summit in Japan’s Hiroshima.

Protesters on Saturday called out Yoon’s “pro-Japan” policy and his inaction to counter Tokyo’s plan to release wastewater stored at the Fukushima nuclear power plant which melted down during the 2011 earthquake and tsunami. The Japanese government has pledged to observe safety standards amid resistance from neighboring countries, saying the million tonnes of wastewater will be discharged after being treated for radioactive material.

In Korea, among the most vocally skeptical of the plan’s safety are Yoon’s political opponents. Saturday’s rally was attended by leaders from three parties considered liberal or on the left, including the main opposition Democratic Party of Korea.

Addressing protesters on Saturday, Democratic Party Chair Rep. Lee Jae-myung accused Yoon and his administration of “abdicating their responsibility to protect the lives and safety of South Koreans” by letting Japan release the wastewater into the Pacific.

“The Japanese government does not have to care for the seas being contaminated and (wants to) dump the wastewater anyway, but the South Korean government has no reason to go along with it," he said.

Lee said that Yoon sending a team of South Korean experts to Japan for its own safety inspection, separately from the one being conducted by the International Atomic Energy Agency, would “only end up justifying the Japanese plan.”

Saturday was only the latest in the series of anti-Yoon protests involving major Democratic Party figures. Lee said that his party would continue to participate in future protests against Yoon and his “diplomacy failures,” adding it was “always the people who took to the streets who came to the country’s rescue in moments of darkness.”

Some of the organizers of the weekly protests calling for Yoon to step down are those who led the protests that led to the impeachment of the last conservative party president, Park Geun-hye.

The ruling party slammed the protests as part of an “attempt to stain the president’s diplomacy feats.”