Korean-American Shin Eun-mi’s deportation from South Korea has revealed a U.S. ally divided over the reach of its National Security Law, with both sides fiercely contesting its proper interpretation and application.

Shin, 53, was deported  earlier in January on charges that she praised the totalitarian North Korean regime in a series of talks, along with leftist activist Hwang Sun who was issued an arrest warrant in South Korea on Jan. 14.

Debate over her case has spilled over to the United States, where Shin was met with clashing banners from liberal and conservative groups upon her arrival at Los Angeles International Airport on Jan. 12.

While some banners called her a “patriot of the people,” others demanded that, “if you like North Korea, return to the North.”

Under South Korean law, the Justice Ministry can order forceful repatriation of any foreign nationals who “pose a threat to the safety of the nation.”

Shin, or Amy Chung, is a legal resident of L.A. who emigrated to the U.S. after graduating from college in Seoul. She then attended the University of Minnesota to complete her master’s and PhD degrees in classical singing, which is where she met her husband, Jung Tae-il, who currently operates a private learning institute in L.A.

Dong-Ah News reported on Jan. 3 that Shin’s husband, Jung, said “the media is overreacting to a ‘dumbhead’ middle-aged woman who just wrote and spoke of her experiences.”

During her public talks across the country, Shin drew on her classic vocal training and allegedly sang a North Korean song that praised former leader Kim Jong-il, father and predecessor of current leader Kim Jong-un. She also said that North Koreans “appeared to be happy” during her three trips to the country between 2011 and 2013.

Such comments led to an outcry from conservative critics and also North Korean defectors, who accused Shin of painting a distorted picture of Kim Jong-un’s dictatorial regime.

Those who denounced Shin were quickly met with backlash from left-wing activists, who criticized the government in Seoul for undermining their rights to freedom of expression, which is guaranteed by Article 21 of the South Korean Constitution.

South Korea technically remains at war with North Korea, since the conflict, which broke out in 1950, ended with a truce instead of a peace treaty in 1953. With the ebb and flow of North Korean bravado and threats ever since, the North remains a sensitive topic in Seoul. South Korean National Security Law bars access to North Korean websites, and jails those who circulate pro-North propaganda.

The National Security Law has come under fire especially from leftist activists who experienced a crippling political loss just one month prior to Shin’s deportation: the Constitutional Court of South Korea ordered the dissolution of a small, extreme leftist party, claiming that it “aimed at using violent means to overthrow our free democratic system” and “ultimately establishing a North Korean-style socialist system.”

The three-year-old United Progressive Party was a minor entity with only five seats in South Korea’s 300-member National Assembly, but the ruling marked a political victory for President Park Geun-hye.

South Korea’s National Security Law was enacted in 1948 with the purpose of “regulating activities that compromise the state’s safety,” amid high tensions on the peninsula during the early stages of the Cold War.

“The government was understandably insecure at the time and tried to deal with what it called communist threats, for it had to compete with the North Korean regime that was established right around the same time,” said Chaihark Hahm, professor of law at Yonsei University in Seoul, in an interview.

President Park has defended the National Security Law, asserting that “unique circumstances on the peninsula warrant, at the very least, a law to guarantee the safety of our country.”

“If a country has certain vulnerabilities, it must have laws to address them. I believe we cannot tolerate parties that disparage the very identity of our country and actively support North Korea,” Park said at a news conference on Jan. 12.

Scott Snyder, senior fellow for Korea studies at the Council on Foreign Relations in Washington D.C., said in a phone interview that President Park’s defense reflected growing domestic friction over whether to get rid of the law.

“The tough part remains how to separate the political suppression piece from the society protection aspect,” he said.

Hahm asserted that South Korea’s National Security Law is not unique “from a comparative point of view.”

“The U.S.’s most recent manifestation of a similar law is the Homeland Security Act. In fact, the concept dates back all the way back to the Alien and Sedition Acts enacted by the Adams administration– and even then, the law was criticized by the domestic opposition, the Jeffersonians,” he said.

Snyder agreed that the comparison was fair. He said he does not expect to “see the U.S. strengthening homeland security laws” in the foreseeable future.

U.S. State Department spokeswoman Jen Psaki expressed mixed views when asked about Shin’s case at a news briefing on Jan. 9.

According to a transcript of the briefing, Psaki said South Korea’s “National Security Law, as interpreted and implied, in some cases, limits freedom of expression and restricts access to the Internet.” But she added that “the Republic of Korea has shown a consistent and longstanding commitment to the promotion and protection of human rights” and “a strong record on human rights and freedom of expression.

Snyder said Shin’s case would have “a very limited impact” on the U.S.-South Korea alliance.

“The two countries have pretty well-coordinated positions on how to approach North Korea, and I don’t see a big gap on how they view the North,” he said.

Hahm agreed that Shin’s case was in fact “a much more domestic issue” with “little relation or ramification in terms of the North-South relationship.” North Korea has not commented on Shin’s deportation.

“It’s more about how mature this society is as a democracy, and I think the U.S. was just trying to express that they would like their ally to uphold mature democratic ideals,” he said.

In the U.S., Shin’s specific plans are unknown. After exiting her investigation at the Korean Immigration Service in Seoul on Jan. 10, she told reporters that she would “make an effort for peace and unification on the Korean peninsula.”

Under the Justice Ministry’s decision, Shin is banned from entering South Korea for five years.