After decades South Korea has banned the sending anti-Pyongyang leaflets into North Korea.
Activists would usually tie leaflets to balloons and float them over the border for North Korean residents to find.
The new law, which takes effect in three months, also stops campaigners sending money, goods and USB drives containing news and information.
Rights activists have said the law is a violation of freedom of speech.
Breaking the law passed by the South’s parliament will be punishable by up to three years in prison or a fine of USD $27,500.
The law was introduced in June after Kim Yo-jong, sister of North Korean leader Kim Jong-un who holds a powerful position in the North Korean government issued a long statement, blaming “defectors from the North” for sending leaflets attached to balloons.
“I wonder if the world knows what kind of riff-raff those foolish defectors are,” said the statement, translated by KCNA Watch.
The North has also sent its own leaflets on helium balloons across the border in the past.
Many of the balloons failed to make it over the border and ended up causing pollution inside South Korea, while also putting a burden upon local people to dispose of them, a spokesperson for the Ministry of Unification said at the time.
In 2014 North Korean soldiers attempted to shoot the balloons down, leading to an exchange of fire across the border.
Seoul has been trying to re-establish ties with Pyongyang after a year of very little contact.