SEOUL—South Korea’s compulsory military service, long regarded as sacrosanct in a nation still technically at war with North Korea, faces a legal test over whether citizens can refuse to serve because of their beliefs.

An army stint is a rite of passage for most young men here, where conscription has existed since 1949 and military influence extends well beyond the barracks. Schools and companies arrange three-day boot camps for workers and students to experience military life. Television shows feature celebrities enlisting in the army. In the workplace, a direct supervisor is commonly called a “marksman.”

That culture has left little room for conscientious objection. The country imprisons more young men for refusing the draft than the rest of the world combined, according to Amnesty International, which said in a February report that about 400 were behind bars last year. Women are exempt from service.

The draft has made South Korea a garrison state, said Park Min-young, a culture critic. “Military culture seeps into companies, schools and personal relationships here,” he said.

In recent months, though, a judicial rift over the subject has begun to play out in lower courts here, setting up a debate over what many see as a bedrock of Korean society.