KCTU president Han Sang-gyun has been imprisoned since July 2016 for his role in the people's rally in November 2015 against former president Park Guen-hye's government's repressive labour law reforms.
KCTU general secretary Lee Young-joo was arrested in December 2017 after two years of self-imposed house arrest. They are both facing charges for the protest.
The Trades Union Congress, Unite the Union and Amnesty International protested at the Korean embassy, London. TUC president Sally Hunt handed in a letter and met with a senior minister at the embassy and its deputy chief of mission. Read more on the TUC blog.
In Hong Kong, 40 members of the HKCTU and civil society activists staged a demonstration at the Consulate General of the Republic of Korea but were prevented by the police from delivering their petition. Read more here and see the joint statement here
ITF general secretary Steve Cotton welcomed the unions' actions and said: "The eyes of the world on the Winter Olympics in Korea is an opportunity to amplify our demands for justice for Han Sang-gyun and Lee Young-joo.
"They did nothing but exercise their democratic right to freedom of association and peaceful assembly. We will keep up the pressure on Korea until they are free and all charges against them are dropped."
You can still write to the Korean government about this. Go to the ITF campaign page here.