South Korean police have arrested an activist on allegations of praising North Korea, banned under the controversial National Security Act.
Hwang Sung, who is said to have praised the North at public lectures last year, could face up to seven years in jail.
At the weekend, the South expelled Korean American travel writer Shin Eun-mi over similar allegations.
Critics say the national security law, which dates back to 1948, is outdated and used to stifle political debate.
The law bans any perceived support for the North, but has been widely criticised.
Ms Hwang, a former spokesperson for a disbanded leftist party, has caused controversy several times in recent years.
She angered the authorities a decade ago by giving birth to a child during a rare visit by a South Korea citizen to Pyongyang.
And she has since continued a campaign for the unification of the two states.
"Had this been a normal situation, they wouldn't have sought my arrest over a talk show I've been hosting for the past few years," Ms Hwang told reporters.