With anti-refugee rhetoric gaining support among Hungarians, Sunday's referendum is expected to be a big win for Prime Minister Orban.
Hungarians are expected to reject the European Union's migrant quotas in a referendum on Sunday, which should boost Prime Minister Viktor Orban's standing at home and embolden him in his battles with Brussels.
Orban has been in power since 2010 and is one of the toughest opponents of immigration in the EU. Last year he sealed the country's southern borders with a razor-wire fence and thousands of army and police border patrols.
In 2015 hundreds of thousands of refugees fleeing war and poverty in the Middle East and Africa crossed Hungary on their way to richer countries in Western Europe, this year Hungary recorded about 18,000 illegal border crossings.
Orban called on Hungarians to send a message to the EU that its migration policies are flawed and threaten Europe's security in a letter published in a daily newspaper on Saturday.
"We can send the message that it is only up to us, European citizens, whether we can jointly force the Union to come to its senses or let it destroy itself," he wrote in the Magyar Idok.
Orban has said his goal for the next few months is to stop Brussels from imposing rules that would forcefully settle refugees.
Human rights groups have criticised the Hungarian government for stoking fears and xenophobia, and for mistreating refugees on the border.
On Friday in Budapest about 1,500 people protested against the referendum.
Opinion polls show support for a rejection of EU migrant quotas of more than 80 percent among those who say they will vote. But they indicate turnout might not necessarily top the 50 percent required for the poll to be valid.
Voting begins at 04:00 GMT and closes at 17:00 GMT. Preliminary results are expected after 18:00 GMT.
Orban claims mass immigration from the Middle East has increased risk of violent attacks in EU societies,
His anti-refugee rhetoric has been well received at home, cementing his Fidesz party's lead over the opposition.
"We must preserve our Hungarian national character here in the middle of Europe, and all the other European states should also preserve their national characters," resident Judit Hegyi said as she took a leaflet from a Fidesz stall in Budapest in the run-up to the vote.
But others have expressed concern about what they called government propaganda, which they say vilifies refugees and incites hatred.
"We came here so that we would be less ashamed of ourselves on Sunday night," said Zsuzsa Berkesi, 46, a teacher, who demonstrated in the capital on Friday.