She posted on her Facebook account that she would vote against both the constitution and the proposition question calling for a military appointed senate during Sunday’s vote.

"I will go out and use my right to vote to vote against a charter that doesn't fully represent the will of the people," she said.

The government of Yingluck -- the sister of the junta's charismatic nemesis, former Prime Minister Thaksin Shinawatra, who was deposed in a 2006 coup -- was toppled in May 2014 when the military took power in a bloodless coup.

The military had claimed to be stepping in to restore order after months of street protests had deadlocked the country and stagnated the economy.

It insisted that drafting a constitution was one of its priorities before restoring the country to democracy.

Critics, however, accuse the military drafted charter of being undemocratic as it contains a clause for a fully appointed senate, with junta opponents also fearing that it would allow a military officer or a civilian acting on behalf of the military to become premier.

The electoral commission, an official agency, has banned all criticisms of the draft charter, along with the wearing of T-shirts calling for voters to reject the draft at the referendum.