SEOUL — South Korea's ruling party is pushing a law through parliament that would criminalize sending leaflets, flash drives and money to North Korea, in what the opposition calls a "disgraceful submission" to Pyongyang and human rights groups say will stifle freedom of expression and humanitarian work.

The move follows pressure from Kim Yo Jong, the sister of North Korean leader Kim Jong Un, who in June labeled defectors based in South Korea “human scum” and “mongrel dogs” for sending items across the border designed to undermine the North Korean regime. She warned Seoul would face a “dear price” unless it prevented this “wicked and sordid act of hostility.”

President Moon Jae-in’s government, which has made improving relations with North Korea a priority, immediately began cracking down on groups that dispatch such materials across the heavily guarded frontier.

South Korean activists hope floating bottles containing items banned in North Korea will find their way into the hands of regular citizens. (Anna Fifield, Jason Aldag/The Washington Post)

Lawmakers from the ruling Democratic Party then introduced a bill to make it a felony punishable by up to three years in prison to send promotional pamphlets and storage devices such as flash drives, money and other financial benefits to the North without the government’s permission.

When a parliamentary committee endorsed the bill last week, opposition lawmakers staged a walkout, calling it “a disgraceful submission to Kim Yo Jong’s order.” A final vote on the bill, which was scheduled to happen Wednesday, has been obstructed by a filibuster by the main opposition People Power Party but is expected to pass soon.

Lawmaker Song Young-gil, a leading sponsor of the bill, said it was necessary to salvage stalled nuclear negotiations with North Korea. But international NGOs called it a threat to freedom of expression, human rights and humanitarian work.

“The South Korean government should abandon its misguided strategy of trying to win favor with Kim Jong Un by cracking down on its own citizens,” said John Sifton, Asia advocacy director at Human Rights Watch. “Promoting human rights is not at odds with effective foreign policy.”

North Korean defectors and activist groups based in the democratic South have long sent printed materials and digital drives across the border containing anything from political propaganda to South Korean movies and entertainment, which are banned in the totalitarian North.

They also send Bibles, food and medicine, often using balloons, drones or large plastic bottles to carry the items over the militarized land and sea border, in the hope that ordinary people in the North will pick up the materials and learn about the oppression imposed by the regime and the relative poverty of their nation.

It was not clear whether sending Bibles and religious materials would be immediately affected by the ban.

The two countries have remained in a technical state of war since the Korean War ended with an armistice, but no peace treaty, in 1953.

Park Sang-hak, a North Korean defector who has been leading the anti-Pyongyang propaganda campaign for the past 15 years, said he has been warned against sending leaflets across the border since June.

“For all these years, North Korean residents have been brainwashed that the Korean War broke out with a deadly raid by Americans and South Koreans,” he said. “Now as a free citizen of South Korea, I have the mission of liberating my brothers in the North from the information black hole.”

Chun Yung-woo, a conservative former South Korea national security adviser, called the leaflet ban “unscrupulous.”

“The ultimate goal of engaging North Korea is to lead the country to open up and make positive reforms,” he said on YouTube. “Is the Seoul government trying to deny the North Koreans the right to information, and support the oppressive regime?”

Human rights groups and activist groups in South Korea have accused the Moon government of restricting funding, obstructing their activities and generally trying to downplay human rights abuses committed by Kim’s regime since coming to power in 2017.

After Kim Yo Jong’s tirade against the South, a number of North Korea-focused NGOs faced reviews and office inspections from the South Korean authorities, in what human rights groups called “political crackdowns.” The government said the inspections were part of regular interactions with the groups and did not come in response to North Korea’s threats.

The Moon administration also justifies the leaflet ban by saying it is necessary to ensure the safety of South Korean residents who live in the border area.

“The irresponsible leaflet campaign led North Korea to threaten a ‘targeted shooting’ at the origin of the leaflets, which made us residents shudder in fear,” a group of residents in the border village of Gunnae-myeon said in a statement this week.

Activists call that an excuse.

“We activists have been sending leaflets and flash drives to the North for many years without harming the safety of the border residents,” said Park, the defector. “The Moon government is banning it all of a sudden only because Kim Yo Jong complained about it.”

Should the bill pass the final vote despite the ongoing filibuster, the opposition People Power Party said it will challenge the law in South Korea’s Constitutional Court.

Denyer reported from Tokyo.