Denmark goes to the polls on Wednesday in a referendum called to end a three-decade-long exemption from European Union clauses on defense and security.

The vote was called in March after Russia's invasion of Ukraine prompted a rethink of security policy in many European countries.

Why did Denmark call the referendum?

Social Democrat Prime Minister Mette Frederiksen said in calling the referendum that a "Yes" vote would "strengthen our security."

It followed dramatic changes in Europe's security environment in the wake of Russia's attack on Ukraine, as Finland and Sweden moved towards applying to join the NATO military alliance.

Denmark is already a member of the trans-Atlantic alliance but has remained outside the EU's moves toward formulating a common defense policy.

Polls show a clear lead for the "Yes" campaign, suggesting that around 40% of voters favor ending the opt-out and 30% want to retain it. Around a quarter of voters are undecided, according to surveys.

In the final stages of the campaign, the "Yes" camp's messaging was aimed at fighting complacency.

"We must always cast our ballots when there is a vote," Frederiksen said in a final televised debate on Sunday.

"I believe with all my heart that we have to vote yes. At a time when we need to fight for security in Europe, we need to be more united with our neighbors," she said.

"The world is changing, and not in a good way. We need to stand together and strengthen the cooperation that strengthens our security," Jakob Ellemann-Jensen, head of the opposition Liberal
Party, said as he handed out pamphlets on Wednesday morning. 

Why did Denmark have an opt-out?

Denmark's opt-out dates back to 1992 when the Maastricht Treaty was agreed to transform the European Economic Community into the European Union.

Denmark rejected the treaty in a referendum that same year, and as a result obtained exemptions allowing it to remain outside the EU single currency and the bloc's common policies on defense, home affairs and justice.

The treaty was then approved the following year. It means Denmark cannot contribute troops for EU missions such as those in Somalia, Mali and Bosnia, or participate in the formulation of EU defense policy.

At present Denmark's representatives leave the room when the other 26 countries discuss defense issues. 

Who is supporting the 'Yes' and 'No' campaigns?

Eleven of the 14 parties in Denmark's parliament are campaigning for a "yes" vote.

Two far-right, Eurosceptic parties, the Danish People's Party and The New Right, and the far-left Unity List, have urged their supporters to reject the proposal.

One of their arguments is that an EU defense policy might weaken NATO, which Denmark joined in 1949.

"NATO is the guarantor of Denmark's security. It would be totally different if it were decided in Brussels," the head of the Danish People's Party Morten Messerschmitt said during Sunday's debate.

er/nm (AFP, AP)