South Korea's Constitutional Court ruled that a law banning multiple nationality holders who are 18 or older from renouncing Korean citizenship unless they have fulfilled military duty does not conform to the Constitution.

In a seven to two ruling on Thursday, the court said clauses of the Nationality Act imposing obligations and restraints on multiple nationality holders violate the principle of the prohibition of excessive restrictions.

Under the Act, multiple nationality holders subject to South Korea's mandatory military service are required to choose one nationality by March 31 of the year they turn 18.

Should they wish to renounce their Korean citizenship, they must submit the relevant application by the same deadline, but past the deadline, they must first complete their military service or wait until they turn 36, when military obligations expire.

The clauses will become ineffective if they are not revised by September 30, 2022.

In previous cases in 2006 and 2015, the court had ruled that the clauses conform to the Constitution.