Myanmar's opposition cried foul Wednesday after the authorities revoked a prison amnesty granted to one of its members last year as part of widely praised political reforms.
It is the first time since military rule ended two years ago that a dissident's pardon has been overturned.
Nay Myo Zin, 38, served less than a year of a decade-long sentence for writing for exiled media outlet the Democratic Voice of Burma.
But the retired military captain was told on Tuesday that he would have to serve six years of his original sentence because he was recently convicted of defaming the police, according to his wife Zin Myo Maw.
Nay Myo Zin was last week sentenced to three months in jail after allegedly telling farmers in a land dispute in the Irrawaddy delta that local police had accepted bribes, his wife said.
He was due to be released on Tuesday after the farmers paid his fine.
"While we were waiting for his release yesterday at the prison, a local official read out the order of the home affairs minister Ko Ko sentencing him to re-serve six years," she said.
"He didn't commit any crime... I feel very sorry for him," she added, vowing to fight for his release.
Nine Nine, a senior member of Aung San Suu Kyi's National League for Democracy (NLD), condemned the decision and pledged the opposition party's support for its member.
"It's wrong. They (the government) can do whatever they want after they have released people under an amnesty," Nine Nine told AFP.
President Thein Sein has freed hundreds of political prisoners since coming to power in early 2011 as part of sweeping changes that have led to the end of most Western sanctions.
Last month dozens of political prisoners were pardoned a day after the European Union agreed to end almost all sanctions against the former pariah state.
But activists say more than 200 political prisoners remain in jail and accuse Myanmar's government of using a series of headline-grabbing prisoner releases for political gain.