By Agence France-Presse
While the communist country routinely jails critics of its regime, 62-year-old Pham Minh Hoang is the first Vietnam-based dissident to have his citizenship revoked in recent history.
Hoang's wife, Le Thi Kieu Oanh, told AFP police came to their house in Ho Chi Minh city on Friday and took her husband away.
The officers told Oanh he would be deported on Saturday, she said.
"I am very sad... because (authorities) announced to me the Vietnamese government will deport my husband," she told AFP.
Hoang moved to France in 1973 and lived there for 27 years before returning to Vietnam to work as a a mathematics lecturer at the Polytechnic University of Ho Chi Minh City.
He was convicted in 2011 of "attempted subversion" for penning a series of articles that Vietnamese prosecutors said were aimed at overthrowing the government.
He was released from jail after 17 months to serve a three-year term under house arrest and has continued to post criticism of the government on social media.
Vietnam's Ministry of Foreign Affairs defended the move to revoke Hoang's citizenship last week, saying he had "violated the laws many times and seriously violated the national security", without elaborating.
A French diplomatic source said consular officials were in contact with authorities to try and access Hoang, while the French embassy in Hanoi called on Vietnam to respect freedom of expression.
Hoang told AFP this month that his French passport had expired and that he needed to stay in Vietnam to care for his disabled brother and elderly mother-in-law.
His wife said Saturday she would remain in the country to care for the relatives.