While overseas, President Moon electronically signed his administration's proposal for amending the Constitution.
And the bill has now been submitted to the National Assembly, to be reviewed and voted on in the next 60 days.
Opposition parties are firmly against this move by the administration, but the liberal leader released a statement defending it.
Calling it a promise made to the public, he insisted the referendum must take place in tandem with the local elections in June, or else it will cost an extra 110 million U.S. dollars.
President Moon also emphasized the Constitution must reflect the rights of the people and the responsibilities of the government in keeping with the times, describing the last ammendment made 3-decades ago as outdated and incapable of doing so.