A pro-democracy MP in Tonga, Fred Sevele, says he is concerned that members of the Police Special Branch have been attending the movement's meetings.
Mr Sevele says the Police Minister, Clive Edwards, has told him the officers are there to ensure that nothing illegal takes place and that there is no attempt to incite the people.
The concerns come as the movement's representatives hold meetings to gauge people's feelings on controversial constitutional amendments that the government is pushing.
Critics say the changes will severely curb media freedom in Tonga.
Mr Sevele says the police presence at their meetings is unsettling.
"The concern as I see it it's when people see him around at meetings like that it can cause some people not to attend meetings, it can restrict people from expressing their own opinions that may run counter to the views and the pronouncements from the authorities"
Tongan MP, Fred Sevele.
Debate on the constitutional amendments, which have already passed their first reading, will resume next week.