In recent days, opponents organised mass rallies and warned that Croatia would surrender its national sovereignty to the Brussels bureaucracy. This prompted the authorities to make strong statements, warning of negative consequences if EU membership is rejected.
Surveys show 56% of voters support accession, while 33% are against. A majority of 50% +1 is needed for the referendum to back the country's accession, expected on 1 July 2013.
Opponents of the accession warned that the EU was not a representative democracy, but a bureaucratic fortress in which the Council obediently signed all bills prepared by the Commission.
Supporters of the "no" vote also said that the European Parliament had no right to veto those laws. It also raised concerns that Croatia would be forced to cut down its agricultural production and that Croatians would be prevented to work in the EU for the next seven years and that the entire Adriatic coast would be sold to foreigners.
Foreign and European Affairs Minister Vesna Pusić said the referendum was a very important decision for the country and a historic opportunity.
Asked by the press what would happen if the majority voted against accession, she said the whole country would bear the economic consequences of such a decision.
"If in the referendum, the citizens decide that they do not want in the European Union, then we will all bear the economic consequences of this choice," she said.
Pusić added that from the first week, after a "no" vote, the effect would be clearly seen in the collapse of the country's credit ratings as well in the loss of market value of Croatian assets. Then, the effect would be seen in the withdrawal of investments, and consequently the reduction of jobs, she added.
Carl Bildt to the rescue
Swedish Foreign Minister Carl Bildt visited Zagreb four days ahead of the referendum, in an obvious bid to help the pro-Europe camp.
During his official talks, the first after the new Croatian government took office, Bildt said Sweden in the early 1990s was suffering from a deep crisis but after joining the EU in 1994 developed in a "spectacular" way.
In an obvious attempt to counter views that Croatia would lose its sovereignty as an EU member, Bildt said that Croatia would have an important voice in the EU institutions, particularly on regional issues. He added that as an EU member, Croatian would find it easier to solve economic problems faced by both Croatia and the Union.
The strongest argument?
Vladimir Drobnjak, Croatia's chief negotiator with the EU, told an audience in the city of Vukovar that citizens should not fear the EU, because Croatia can always leave the Union.
"If Croatia is one day to consider that option, Article 50 of the Lisbon Treaty gives each member country the right to be able to withdraw from the Union in accordance with its own constitutional requirements," he said.
Asked to comment on views that the eurozone crisis is hardly the best time for Croatia's EU accession, Drobnjak said it should not be forgotten that the EU today accounts for 20% of the world economy, while 7% of the world's population lives within its borders.