For Slovenia, as for the majority of member states who joined the
EU in 2004 and 2007, membership of the European Union means that it is
obliged to establish an appropriate new regime on the EU's external
border (members' borders with non-members - so-called third countries)
in accordance with the acquis. Slovenia has to establish security,
customs and inspection controls on its stretch of the external EU
border with the Republic of Croatia and ensure they meet EU
standards.
Slovenia began the partial enforcement of the provisions of the Schengen acquis when joining the EU on 1 May 2004 - with regard to visa policy and preventing illegal immigration. As citizens of the EU, Slovenian citizens can cross the borders of EU member states more easily. The Austrian, Italian and Hungarian border authorities check only the validity of documents required to cross the border, while at airports Slovenians can cross at those points designated for EU citizens, where only the validity of documents is checked and not whether additional conditions of entry have been met, as is the case with third-country nationals.
The evaluation of the readiness to join the Schengen area, which included a review of the land, sea and air borders, police cooperation, data protection and visa policy, began at the beginning of 2006. On the basis of this evaluation a review on the establishment and use of the Schengen Information System was carried out. On 1 September 2007, Slovenia began to use the system 'SIS I for all'.
On 8 November 2007, the Council of the EU decided that all nine candidates for the enlargement of the Schengen area, including Slovenia, were ready to abolish controls on internal EU borders, both in terms of the physical protection of borders and the uses of the Schengen Information System. Their political decision was confirmed in November by the European Parliament at a plenary meeting in Strasbourg. Finally, the decision to enlarge the Schengen area from 15 to 24 countries was confirmed on 6 December 2007 at a meeting of interior ministers of member states.
Slovenia became part of the Schengen area on 21 December 2007, when border controls at the borders with Austria, Italy and Hungary were abolished. On 30 March 2008 border checks have also been lifted at air borders. This represents the final step in the abolition of controls at internal borders. The decision to abolish controls at airports at a later time has to do with changes in flight schedules, which are made twice a year in spring and in autumn. Apart from that, the reasons are also technical, as the implementation of the Schengen regime at airports imposes a strict separation between passengers on internal Schengen flights and other passengers in international traffic.