Croatians go to the polls Sunday to decide whether to become the 28th member of the European Union.

The referendum on joining the bloc comes as the grouping faces one of its biggest challenges ever — the sovereign debt and banking problems that have moved from one eurozone country to another.

Polls indicate that a majority of the population will vote in favor of joining the EU despite Europe's financial problems.

But a sizeable number of Croats oppose the move. On Saturday, police clashed with nationalist protesters in the capital, Zagreb, at an anti-EU rally attended by hundreds of people.

The protesters, many of them independence war veterans, carried banners saying “No to EU'' or “I love Croatia,'' and chanting anti-EU slogans. Using loudspeakers, activists demanded postponement of the vote, arguing that political leaders did not bother to explain about the bloc.

Police arrested several protesters who tried to take down an EU flag from a pole, while others chanted “Treason! Treason!” News reports say a few people were injured during the clashes.

Croatia has gone through an arduous six-year negotiating process with the EU before signing an accession treaty last year. It is set to join the 27-nation block in July 2013.

But in recent years, a growing number of Croatian citizens have grown disillusioned with the union and many believe there is nothing to be gained by joining, while they say some hard-earned independence may be lost.

Opponents of the accession singled out Foreign Minister Vesna Pusic as the main target of their criticism as she has been one of the main negotiators in the entry talks. She has said that postponing the referendum could have disastrous consequences for the country's economy.

The Balkan nation is faced with serious economic problems, including unemployment at around 17 percent and a budget gap, projected at more than 6 percent of its gross domestic product.

In addition to the referendum, the accession treaty has to be ratified by all 27 member states before Croatia can enter the bloc.

Of the six former Yugoslav republics, only Slovenia is an EU member, having entered the grouping in 2004.