A resolution passed through the European Parliament by a vote of 483-95, with 65 abstentions, for an in-depth investigation into a surveillance program said to have targeted EU institutions.
European lawmakers began pressing the issue during plenary debates in June. Details of a broad computer-based surveillance program dubbed Prism were revealed to the media by former U.S. National Security Agency employee Edward Snowden.
German newspaper Der Spiegel reported last month the surveillance program extended to EU computer systems. Catherine Ashton, the top foreign policy chief for the EU, said she wanted "urgent clarification" on the issue when the allegations surfaced.
Members of Parliament expressed "grave concern" about allegations similar programs are operated by EU member states Great Britain, Sweden, the Netherlands and Germany.
Parliament's Civil Liberties Committee said Monday it would gather information during the inquiry from U.S. and European sources and present its findings by the end of the year.
Members said it would be "unfortunate" if trade talks with the United States were affected by the spy allegations.