Taiwanese writer and former Hong Kong resident, Chang Tieh-chi, has been denied entry to into the SAR.
In a message posted on his Twitter account, the human rights and democracy activist said immigration officers banned him from entering the city and only let in his Hong Kong wife.
Chang used to be the chief editor of City Magazine and lived in Hong Kong. He was coming to take part in a forum being organised here.
Civic Party lawmaker Kwok Ka-ki said the ban on Chang was beyond reason, as he has no official position in any political organisation.
Kwok said Chang as a past editor of a progressive magazine had written a lot on the relationship between Hong Kong, Taiwan and China. The only possible reason to deny him entry will be his opinions or articles, the lawmaker said.
He said this incident, and the ban on UK politician Benedict Rogers earlier this year, shows that if you write anything against the wishes of those in power in the SAR and in Beijing, you will end up being denied entry to Hong Kong.
He also said the ban harms Hong Kong's international image and the "One Country, Two Systems" principle.