Opposition lawmakers accused Ms. Park and her party of trying to divert attention from her election scandal by moving against the minor United Progressive Party, first with the arrest of its members on highly unusual charges of treason and now with a lawsuit to disband their party.

The recent scandals showed that South Korean politics remains deeply divided and volatile over North Korea six decades after the Korean War of 1950-53 ended without a peace treaty. They also raised questions about how freely people can talk about North Korea in the South, where the government blocks access to North Korean websites and people are still arrested for resending Twitter posts of North Korean propaganda materials.

The United Progressive Party, with six seats, represents a minor force in the 299-member National Assembly. The main opposition party regarded it as too radical and kept it at a distance.

But the political firestorm over its fate reflects a larger struggle between liberals and conservatives in South Korea. The liberals stress the “nation” and reconciliation with North Korea, while the conservatives place anti-Communism at the center of their identity. The strife between the two camps intensified with the election of Ms. Park, whose father remains a godlike father figure among conservatives.

Some of the United Progressive Party members feared that if there were another war on the peninsula, conservatives would round up leftists for mass executions, “as Jews were once rounded up,” according to the transcript of a secret meeting of party members in May that was submitted to the court for the trial of party members on treason charges. Avoiding such a fate was cited as one of the reasons of plotting an armed rebellion.

The far left party’s platform calls for “rectifying our nation’s shameful history tainted by imperialist invasions, the national divide, military dictatorship, the tyranny and plunder of transnational monopoly capital and chaebol,” the latter referring to South Korea’s giant family-controlled business conglomerates which began expanding its influence under Ms. Park’s father. The party wants to end the American military presence, dismantle South Korea’s “subordinate alliance with the United States” and unify the North and the South.

The conservative ruling party has long accused members of the United Progressive Party of subscribing to North Korea’s ideology of juche, or self-reliance, and has called for its disbandment.