Europe's highest court is set to consider whether Facebook illegally allowed the NSA to spy on its European users.
The European High Court will try to determine whether or not the social network transferred masses of user data to US intelligence services after Ireland's High Court adjourned a privacy campaigner's case, pending European judges' findings.
Campaigner Max Schrems contends that Ireland's data protection commissioner had incorrectly refused to investigate claims that Facebook's Dublin base had illegally sent user data to the NSA under the latter's Prism surveillance programme.
Now Europe will decide whether Irish regulators should investigate the data transfers or not, which were permitted under a US-European agreement that relies on the assumption that US privacy protections are equivalent to those in the EU.
Schrems took the Irish data regulator to court after it dismissed his claims that a loophole in the agreement - revealed by whistleblower Edward Snowden - meant that the NSA conducted "mass and largely unsupervised surveillance" of Facebook user data.
And the Irish judge, Gerard Hogan, said the revelations had exposed holes in American data protection that could undermine the US-EU agreement.
Facebook's European operations are centred in Dublin. The company has previously stated that the US government does not have access to its servers, and that it hands over data only when lawful requests are made.
"This is the best outcome we could have wished for," Schrems said in a statement. "This could get the transatlantic discussion to a whole new level."