Differences of opinion between Member States led to a deadlock in the abolition of border controls within the Community, but in 1985 five of the ten Member States at the time – Belgium, France, Luxembourg, the Netherlands and West Germany – signed an agreement on the phasing out of border controls. The agreement was signed on the princess Marie-Astrid boat in Moselle, near the city of Schengen, where the territories of France, Germany and Luxembourg meet. Three of the signatories, Belgium, Luxembourg and the Netherlands, had already abolished common border controls under the Benelux Economic Union. [Citation required] In December 1996, two non-EU states, Norway and Iceland, signed an association agreement with the countries that signed the Schengen accession agreement. Although this agreement never entered into force, the two countries were part of the Schengen area following similar agreements with the EU.  The Schengen Agreement itself was not signed by non-EU states.  In 2009, Switzerland officially concluded its accession to the Schengen area by adopting an association agreement by referendum in 2005.  From 2000 and 2002, the United Kingdom and Ireland participated in certain aspects of the Schengen Agreement, such as the Schengen Information System (SIS). The Schengen Agreement and its implementing agreement were adopted only for some signatories in 1995, but just over two years later, at the Amsterdam Intergovernmental Conference, all the Member States of the European Union, with the exception of the United Kingdom and Ireland, had signed the agreement.
During these negotiations, which culminated in the Treaty of Amsterdam, it was agreed to integrate the Schengen acquis into the main body of EU law, along with opt-outs for Ireland and the United Kingdom (which withdrew from the EU in 2020) to leave the Schengen area.  The Schengen area originally had its legal base outside the European Economic Community at the time, since it was created by a subgroup of Community Member States with two international agreements: all persons who crossed external borders, at the entrance or exit, are subject to the control of a border guard. The only exception applies to regular border workers (with a right of free movement or third-country nationals) well known to border guards: once an initial check has revealed that there is no reporting in the Schengen information system or in national databases, they can only occasionally be subjected to “random” checks instead of systematic checks each time they cross the border.    The question of whether the current situation still justifies internal border controls is the subject of political debate.