BRUSSELS — The European Union’s top court says in an advisory opinion that a deal between the EU and Canada on sharing airline passenger data breaches citizens’ privacy and cannot be concluded in its current form.

Wednesday’s opinion by the European Union Court of Justice’s Advocate General Yves Bot was a setback to attempts to share airline data in the fight against extremism.

It says that transferring passenger data from the EU to Canada and the possibility that the information could be shared with others “entail an interference with the fundamental right to respect for private life.”

The EU and Canada signed the agreement in 2014, but the European Parliament subsequently referred it to the court for a ruling on whether it was compatible with EU privacy laws.