Twaweza's executive director Aidan Eyakuze says the Tanzanian government has confiscated his passport and barred him from leaving the country.
Mr Eyakuze revealed this during a press conference in Dar es Salaam on Friday.
The not-for-profit research firm released findings early last month that showed President John Magufuli’s popularity had plummeted to 55 per cent this year from a high of 96 per cent in 2016. In 2017, the ratings stood at 71 per cent.
The report put Twaweza in a collision course with the Commission for Science and Technology (Costech) after the government agency served the pollster with letters accusing it of conducting
research without a permit and demanding a response on why disciplinary action should not be taken against it.
"They did not tell me what was the reason behind confiscating my passport and why they did not want me to travel outside the country," Mr Eyakuze said on Friday.
As a result, he said, he failed to attend organisation's meetings at its offices in Kampala and Nairobi.
The Twaweza boss said he even tried to apply for a temporary travel documents but was denied.
“We are not aware of any court order mandating this restriction of travels outside Tanzania, but we do not feel intimidated or threatened by such actions,” he said.