A US-EU commercial data-sharing deal faces a major test on Wednesday when an adviser to the European Union’s top court will say whether he believes it is still binding in light of allegations of mass US spying.

The case stems from a complaint filed by 27-year-old Austrian law student Max Schrems against Facebook with the Irish data protection commissioner, who monitors compliance with privacy laws. Schrems argued the company helped the US National Security Agency (NSA) harvest email and other private data from European citizens by forwarding data to servers in the United States and asked the Irish watchdog to investigate whether the United States was providing adequate data protection.

The Irish regulator rejected the request on the grounds that it was bound by the EU Safe Harbour agreement of 2000 - which allows companies to transfer EU citizens’ data to the United States because it is held to have sufficient privacy safeguards in place. The Irish watchdog plays a central role because Facebook users in the EU enter an agreement with Facebook Ireland when they join the social network.

Safe Harbour, which simplifies the everyday business of some 4,000 companies, came under fire in 2013 after fugitive ex-NSA contractor Edward Snowden leaked details of a US mass electronic surveillance programme, known as Prism. The leaks showed the NSA used major web companies, including Apple, Google, Facebook and Microsoft, to gather user data. The European Commission subsequently called for a review of the agreement and negotiations with Washington have been going on since January 2014.

Wednesday's opinion to judges, who are expected to rule in a few months' time, could have an impact on the talks. Schrems, who still uses Facebook and says he wants to improve it, appealed to the Irish High Court in October 2013. In his referral, High Court Justice Gerard Hogan upheld the Irish data protection commissioner's claim that it did not have the authority to investigate because of Safe Harbour. But he asked the European Court of Justice (ECJ) in Luxembourg if the Irish regulator was still bound to follow the Safe Harbour decision given "gaping holes in contemporary US data protection practice" and whether it could or should conduct its own investigation in light of the Snowden allegations. ECJ Advocate General Yves Bot will deliver his opinion on Wednesday at around 0930 CET (0730 GMT).

While the court’s judges are not bound by the opinion, they follow it in most cases. Facebook declined comment.

Bloomberg