Transitional president General Mahamat Idriss Deby Itno, whose junta has governed since 2021, had promised to hand power to civilians and hold elections this year before postponing them to 2024.
More than 8.3 million people in the vast but poor Sahel country are called on to vote in a referendum slated for December 17, in a key step towards the elections and establishing civilian rule.
The opposition, NGOs and political scientists say the ballot looks set to be about maintaining Itno and his family's "dynasty" after the three decades of absolute power enjoyed by his father Idriss Deby Itno.
"Beyond what form the state takes, the main issue is to allow power to test its popularity and its legitimacy, which will be determined by the turnout rate," Issa Job, professor of law at the University of N'Djamena, told AFP.
"The form of the state is not the priority," added Enock Djondang, former chairman of the Chadian League for Human Rights (LTDH).
"All those who reject this regime can only vote against what he proposes."
The new proposed constitution is not greatly different from the previous one, which concentrated significant powers in the hands of the head of state.
The pro-junta "Yes" camp supports a unitary state, while opponents back a federal model.
The most radical opposition groups, some of whose leaders have gone into exile since the bloody repression of a demonstration on October 20, 2022, urge a boycott of what they term a "masquerade."
What is proposed is a "solitary electoral process" for the "perpetuation of a dynastic system," according to the Consultation Group of Political Actors (GCAP), a platform of some 20 parties.
'Free' elections
On April 20, 2021, a 15-strong junta of generals proclaimed 37-year-old general Mahamat Deby as president for a transition period after his father fell on the front line while accompanying troops against rebels.
Deby junior promised on taking over to hand back power to civilians as well as allow "free" elections after an 18-month "transition" period.
He also pledged not to stand himself.
But 18 months later, on the recommendation of a national dialogue boycotted by the vast majority of the opposition and the most powerful rebel groups, Mahamat Deby extended the transitional period by two years.
He also allowed himself to stand for election as president, swapping his army uniform for civilian garb.
'Massacre'
Mass protests broke out in October last year after the extension of the transition period and were brutally suppressed by the security forces.
Between 100 and 300 people were shot dead by police, according to the opposition and NGOs, as people protested in the capital N'Djamena and beyond.
The authorities say around 50 died -- including six members of security forces.
On Thursday, the government handed an amnesty to "all civilians and soldiers" implicated in the disorder, indicating the junta's "desire for national reconciliation."
The opposition protested at the idea of a law for a general amnesty designed to "protect from justice the police and soldiers behind the massacre."
All anti-regime protests have been summarily declared illegal over the past year, save for one drawing key opposition figure Succes Masra, who has returned from exile after signing a "reconciliation" accord with Deby.
On October 13, Human Rights Watch (HRW) voiced concern at "attempts to limit political dissidence before the referendum."
"For this referendum to have any legitimacy, opposition parties and their leaders must feel free to meet and campaign. Otherwise, the referendum risks being seen as a means to make the transitional government into a permanent one."
Chad's 18 million-strong population is divided between its arid north and Muslim population, which has dominated power for more than 40 years, and a more fertile south mainly home to Christians and animists.
Chad last year was ranked the second-lowest country in the world in the UN Human Development Index and 167th out of 180 nations regarding the perception of corruption by Transparency International.
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