Chileans are voting in a referendum to decide whether to adopt a new constitution to replace the one brought in under Gen Augusto Pinochet.
A previous draft put forward by an elected body dominated by left-wing delegates was rejected last year.
A constitutional council, this time dominated by right-wing delegates, has drafted a new, more conservative version.
But polls suggest Chileans remain divided on whether to approve it.
The drive for a new constitution started in 2019 after massive anti-government protests rocked Chile, which is normally seen as a haven of stability in the region.
The protesters, many of whom were left-wing students, demanded drastic social and political change.
After months of disruption, the conservative president at the time, Sebastián Piñera, agreed to launch a process to rewrite the 1980 constitution.
But the first draft, crafted by a constitutional convention chosen by voters, proved too radical for many.
Many balked at its sweeping reforms and its proposals to change many of the country’s established institutions, such as replacing the 200-year-old Senate with a new Chamber of Regions.
It also proposed declaring Chile a “plurinational state”, recognising the rights of Chile’s indigenous groups – which make up about 13% of the population – to their lands and resources.
In September 2022 it was rejected by 62% of voters.
A new constitutional council – this time made up of 24 individuals designated by Congress and 51 representatives elected by the Chilean people – was created to come up with a new draft.
It is this revised draft which Chileans have been asked to approve or reject this Sunday.
Opinion polls suggest that this second draft may also fail to get the backing necessary for it to come into force, with 46% telling pollsters they plan to vote against the draft and only 38% saying they will back it, with 16% still undecided.
While the first draft was widely criticised for being “too far-left”, some voters have said that this second draft has veered too far to the right.
Socialist Party Senator Paulina Vodanovic warned that the new text represented “a move backwards” on many aspects of Chilean social and political life, such as gender issues. Other leftist critics argue that the revised proposal fails to adequately protect indigenous rights.
On the issue of abortion, for example, left-wing critics deem the proposed text too ambiguous and say it could allow future restrictions on existing reproductive rights.
Left-wing critics also dislike the weight given to private property rights and the fact that the new text enshrines private sector participation in the provision of basic services such as health, education or pensions.
Some describe it as being more conservative than the current constitution it aims to replace.
Proponents of the new draft say it gives individuals more choice by letting them decide if they prefer public or private providers for basic services.
Natalia González, a member of the constitutional council, wrote on X, formerly Twitter: “If the state does it well, then they [the Chilean people] can opt for it, but if not, people don’t have to remain captive. That freedom is protected in the new constitution.”
The far-right Republican party, which holds a majority of the seats on the constitutional council, is backing the new draft.
The party’s leader and former presidential candidate, José Antonio Kast, urged “us Chileans who last year voted ‘reject’, now have to vote in favour, in favour of change, in favour of improvement”.
The government of President Gabriel Boric, the left-wing former student leader who beat Mr Kast in 2021, has been accused by the opposition of openly promoting the “reject” option.
President Boric has already said that if the new draft is rejected, he will not push for another rewrite.
In that case, the current constitution will remain in place, although amendments and changes could be proposed.