Lawmakers attend the National Assembly's plenary session in its main building in Seoul, Monday. Yonhap

South Korea's parliament on Monday passed a controversial bill prohibiting the launching of anti-Pyongyang leaflets across the inter-Korean border, a move critics say violates freedom of expression.

The revision to the Development of Inter-Korean Relations Act, billed as the anti-leaflet law, outlaws the scattering of leaflets critical of North Korean leader Kim Jong-un or his political system across the border.

Violators of the law can face up to three years in prison or a fine of up to 30 million won (US$27,000), if convicted.

The bill was passed during the National Assembly's plenary session in a 187-0 vote, one day after lawmakers of the conservative main opposition People Power Party (PPP) staged a filibuster to block its passage.

The passage came six months after Kim Yo-jong, the powerful sister of North Korean leader Kim Jong-un, threatened to scrap a no-hostility military pact with South Korea in anger over anti-Pyongyang leaflets.

The two Koreas agreed to suspend leafleting and other hostile acts in the border area in the Panmunjom Declaration adopted by their leaders in 2018.