Prime Minister Mette Frederiksen called on Sunday for citizens to vote to overturn Denmark’s opt-out from EU defence policy in a referendum to be held on June 1st, following Russia’s invasion of Ukraine.

Denmark’s opt-out – retsforbehold in Danish – is one of four EU special arrangements negotiated by the Scandinavian country, and has seen it abstain from participation in EU military operations and from providing support or supplies to EU-led defence efforts.

READ ALSO: Denmark to hold referendum on scrapping EU defence opt-out

After the Danish public voted to reject the Maastricht Treaty in June 1992, Copenhagen obtained opt-outs in four sovereign areas: the single currency, justice and police matters, and EU citizenship along with defence, the opt-out which will be the subject of the June referendum.

The opt-outs mean, broadly, that Denmark is not obliged to follow EU laws on these areas and is also not involved in forming the laws – its ministers and officials do not participate in EU ministerial meetings in these areas.

The upcoming referendum will be the ninth to be held in the Denmark since it voted in favour of EU (then European Community) membership in 1972.

In December 2015, the Danes voted no in a referendum on the police and justice opt-out which would have strengthened the country’s cooperation with the European Union on those matters. Concerns about losing their sovereignty over immigration were a key factor in the ‘no’ vote.

Single currency

The single currency opt-out means that Denmark is not obliged to join the euro. The country has kept the krone as its currency and is also allowed to practice independent fiscal policy under the terms of the opt-out.

Although Denmark has not introduced the euro, it does participate in some areas of the single currency. For example, an agreement between the Danish central bank, Nationalbanken and the European Central Bank (ECB) means that the exchange rate of the krone follows that of the euro. When the ECB increases or cuts interest rates, Nationalbanken will do the same.

The exchange rate between the krone and the euro is also maintained at a very constant rate, echoing the relation between the krone and the Deutschmark in pre-euro times.

Meanwhile, Denmark cannot be sanctioned by the EU if its budget gives too high a deficit, unlike eurozone countries.

Danes voted no to ending this opt-out and taking on the single currency in a close referendum in 2000, in which 53.2 percent voted to keep the krone and 46.8 percent voted in favour of introducing the euro. Turnout was 87.6 percent.

Defence

The opt-out that will be in question in June’s referendum, defence, means that Denmark does not generally participate in the EU’s foreign and security policies in relation to defence, and is not involved in voting for those policies but can be involved in more general discussions of EU defence policies.

This means Denmark neither finances nor participates in any military operations conducted by the EU, and would not provide troops or equipment to EU-led missions in conflict zones.

Denmark does, however, take part in civil operations, which up to now have formed the bulk of EU military activities. The EU does not have its own army but EU member states’ military forces can work together under EU auspices.

Justice and police

This opt-out, which Danes voted to retain in a 2015 referendum (see above), means that Denmark in principle is outside of the EU cooperation on laws relating to border control, asylum, civil law, criminal law and cross-border crime. There are two important exceptions: visa rules and the Schengen area, in which Denmark participates fully.

The result of the 2015 referendum meant that Denmark chose not to replace its current blanket opt-out of EU justice rules with a model which would have allowed it to choose whether or not to participate in some areas of EU policy on a case-by-case basis – in other words, an “opt-in” model.

The justice and police opt-out means that Denmark does not participate Europol, the EU’s international policing and data resource-sharing organisation. Denmark does have some level of cooperation with Europol however, agreed following negotiations subsequent to the referendum.

EU citizenship

The final Danish opt-out, which relates to EU citizenship, does not have any practical effect.

The opt-out was adopted by Denmark to guarantee that EU membership would not eventually take the form of a national citizenship or an equivalent of this. This guarantee is now written into the EU treaty so that it applies for all member countries: EU citizenship is a supplement to national citizenship and does not replace it.