Big spending on schools, roads and hospitals have underpinned Correa's popularity among the poor and lower middle classes, but rivals accuse him of having an authoritarian streak and using public votes to amass power.
Poll shows around 55-60 percent of voters are in favour of the referendum
However, stronger campaigning by Correa's rivals in the past few days has boosted the 'No' campaign leaving them about 10 points behind.
The most controversial two proposals set the foundations for a new justice system in which Correa will have more direct say over appointments. He argues that corrupt judges have to go so that police can better fight crime, a huge concern in the Andean country of 14 million people.
"Some are saying this is a totalitarian state in which things are done by force. Here we're doing it with a (public) vote, the most democratic way there is," Correa said.