They were among 21 Red Shirt supporters charged with trespassing, arson, breaking security laws and terrorism over an attack on a provincial hall in Ubon Ratchathani in northeast Thailand in May 2010.
“Four were found guilty and sentenced to life in prison, but as they cooperated the court commuted the sentence to 34 years,” an official at the Ubon Ratchathani provincial court told AFP after Wednesday’s ruling.
Nine other defendants were acquitted due to a lack of evidence while the rest were handed prison sentences ranging from eight months to two years.
“I respect the ruling but in my opinion I think the punishment is too harsh,” said Red Shirt chairwoman Thida Thavornsert, saying that the accused were motivated by a desire for political change.
“We will appeal,” she added.
The Red Shirts, who are broadly loyal to ousted fugitive premier Thaksin Shinawatra, held two months of protests in Bangkok last year that sparked a military crackdown which left more than 90 people dead, mostly civilians.
The violence also spread outside the capital, mostly to the Red Shirts’ stronghold in the northeast, including Ubon Ratchathani.
The Red Shirts were campaigning for early elections, accusing the then-government of being an unelected elite, because it came to power after a court ruling ousted allies of their hero Thaksin.
Thaksin’s sister Yingluck Shinawatra is now prime minister after his party staged a comeback with a major victory in a general election last month.