Former Cosatu general secretary Zwelinzima Vavi and EFF leader Julius Malema are plotting to overthr.
The leader of the ring, Tran Hoang Anh, 42, was sentenced to 20 years in jail at the end of the week-long trial Wednesday before the Hanoi People's Court, the newspaper Phap Luat reported.
Eight other defendants received 18 to 26 years in prison while 18 were sentenced to three to 16 years in prison. Another two received suspended sentences, the police-run newspaper An Ninh Thu Do said.
The ring lured young women and girls from poor villages in the north of the country with promises of well-paid work and sold them to brothels in China and Vietnam.
The suspects were convicted of crimes in connection with the trafficking of nine women and 20 minors from February 2009 to July 2010.
Police rescued 15 of those victims, all of whom were younger than 16.
The ring was uncovered in 2010 when a 17-year-old girl cried for help as a gang member was queuing for train tickets to take her forcibly from Hanoi to Lao Cai province on the Chinese border.
Human trafficking is widespread in Vietnam, where high unemployment in rural areas drives many people to migrate.