Twenty-three civil society groups have launched a campaign against the Burundi government's plan to amend the Constitution to enable President Pierre Nkurunziza to run in the 2020 elections.
The civil society organisations, whose registration was revoked for allegedly supporting the failed 2015 coup, say the deregistration was an effort for the incumbent president to remain in power.
"We believe that the referendum cannot be fair so long as it is conducted and managed by the same commission that approved the unconstitutional candidature of President Nkurunziza in 2015," said Vital Nshimirimana, one of the leaders of the civil society organisations who is currently in exile.
Mr Nshimirimana said the civil society will create awareness among the citizens so that they can adopt a common approach against the constitutional amendments.
President Nkurunziza recently launched a countrywide campaign on the draft Constitution. The Constitution was last amended in 2005.
Top government officials have been going round the country educating the public about the draft. Ombudsman Edward Nduwimana told Burundians to vote for Yes in the May referendum.
Critics say that the government is involved in premature campaign, while the law allows parties to campaign for only two weeks prior to the referendum.
The National Independent Electoral Commission said it has no power to stop the government from campaigning even as members of the opposition have been arrested for campaigning against the review.
Agathon Rwasa, opposition leader and the deputy speaker of the parliament, said more than 20 of his supporters have been arrested since last week on accusations of campaigning against the constitution amendment.
"It is just simple allegations because they know we are opposed to that Bill so they are trying to harass us," said Mr Rwasa.