With just a week to go, Yes and No campaigners were out on the streets of Istanbul and the rest of the country on Sunday.
In the Yes camp are Erdogan's Justice and Development Party (AKP), backed by the hard-right Nationalist Movement Party (MHP).
In the No camp are the Republican People's Party (CHP) and left-wing parties, most notably the pro-Kurd People's Democratic Party (HDP).
CHP activists in Istanbul's Sisli district insisted they were confident the No would win.
But they said the campaign was an uphill battle.
"AKP uses everything, especially money, and they don't give any money to CHP," said CHP veteran Kamer Demir. "So we cannot talk to our people, we cannot tell our things to people."
The claim of unequal resources is borne out by the relative share of banners draped across the streets.
"You see lots of Yes brochures and billboards outside. Did you see No anywhere?" asks Yasemin Bektas of the Women Say No campaign. "It doesn't mean we are not working. They are not giving us permission to work. It's not legally but you feel the pressure on you."
With thousands of government employees purged after last year's failed coup, the AKP’s opponents accused the ruling party of abusing its power to influence the vote.
CHP campaigner, Emre, is a doctor in a public hospital.
"Some staff related to the government, they can say yes in the duty time,” he told RFI. “Unfortunately I can't say no with little words because my work is under threat."
The HDP, which been seen as a serious threat to the AKP since its candidate, Selahuttin Dermitas, won nearly 10 percent in the 2014 presidential election, has the target of severe repression since the government broke off the peace process with the Kurdistan Workers' Party (PKK) guerrilla group the following year.
Many of its members have been jailed, including 12 of its MPs, among them Dermitas, accused of complicity with the PKK.
In the heated rhetoric that has become his trademark, Erdogan has said that a No vote would help the “terrorists”, by which he means not only the PKK but also the Islamic State armed group, which has staged several deadly attacks on Turkish soil, and the organisation of US-based preacher Fehtullah Gulen, which the government says was behind last year’s failed coup.
Since then a state of emergency has been declared and thousands have been jailed or purged from jobs in the state and private sectors.
And over 100 media outlets have been closed because of alleged ties to the coup plotters or the Kurdish rebels.
"We have dozens of journalists behind bars for eight months, since the state of emergency,” Erol Onderoglu of Reporters Without Borders points out. “And these journalists are considered to be in a way hostages of this referendum. I think there is a total contradiction between the process like the referendum needs and what we are facing on the ground, reducing media outlets and jailing journalists in a systematic manner."
The satirical paper Penguen has calculated that the Yes campaign has received 10 times more live airtime on television than the No campaign and papers and magazines that take a line independent of the government’s have been reduced to a handful.
Nevertheless, opinion polls show the two sides at 50-50.
So the campaign may get even tougher over the next week.
To read our coverage of Turkey's referendum click here.