BANGKOK (Reuters) - Preparations by Thailand's junta for a referendum in August over a new Constitution that critics fear will entrench the military's influence were stepped up on Wednesday (June 15) as military cadets were shown what to do at polling stations on the day.

Prime Minister Prayut Chan-ocha's junta has ordered some 100,000 cadets - high-school and university student volunteers - to carry the message to people that they have a responsibility to vote.

Critics among civilian politicians, however, fear that the cadets are being used to convince Thais to vote in favour of the military-backed charter, in contravention of rules issued in May that bars anyone from campaigning for either side in the run up to the referendum on Aug 7.

The junta has threatened to jail anyone who violates that rule for up to 10 years.

Opening the training session at a Bangkok hotel, Prawit Rattanapian, an Election Commissioner, said the cadets' role was only to encourage people to vote. "The student volunteers will not explain whether the constitution is good or bad but will invite people to exercise their right to vote," Mr Prawit told Reuters.

As he spoke, cadets, in their green uniforms, were familiarised with mock polling booths, where they will be expected to assist voters, particularly the elderly and disabled, on polling day.

Mr Chatree Pensomboon, a second-year student soldier from Marialai School in Bangkok, said he did not think he was being asked to do anything political. "I look at this as a kind of social work," he said.

Thailand's generals seized power in bloodless coup two years ago, saying their action was needed to end months of street protests that had paralysed the government and hobbled the economy.

During a decade of unrest, political divisions in Thailand have broadly pitted the military, bureaucrats and the middle class against supporters of populist governments that were overthrown by coups in 2006 and 2014.