With invitation to Latvia for accession to the European Union (EU) received on 13 December 2002 in Copenhagen, as one of the most important issues of domestic policy became arrangements for a referendum on joining the EU. Referendum took place on September 20, 2003.

On May 15, 2003 the Parliament of Latvia approved amendments to the Constitution of the Republic of Latvia /Satversme/ and in the Law "On National Referendum and Legislative Initiatives", thereby securing the legal base for referendum on membership of Latvia in the EU.

The amendments supported by Parliament provide that membership of Latvia in the EU shall be adjudicated in referendum initiated by Parliament and that the decision on membership of Latvia in the EU referred for the referendum has been adopted if the number of voters is at least one half from the poll that took part in the latest Parliament elections and if the majority has voted for membership of Latvia in the EU.

In compliance with Article 38 of The Saeima Election Law, the total amount of valid election envelopes shall be deemed as the total number of voters that took part in the previous elections. Since in the latest elections to 8th Saeima 995,085 valid election envelopes were received, the referendum on membership of Latvia in the EU would be accomplished if at least 497,543 voters will participate in it.

If the referendum is counted as accomplished, the outcome is determined by the majority voting. Namely, membership in the EU is supported, if at least one half and one from all of the referendum participants vote "for". Membership in the EU is not be supported, if "for" vote exactly one half or less than a half from all of the referendum participants.

In the referendum the voters had to reply to the question: Do you support a membership of Latvia in the European Union?.