Europe's top court will give an opinion on December 12th on Austrian privacy activist Max Schrems' landmark case against Facebook, which will affect how hundreds of thousands of companies transfer personal data worldwide.

The date was set at the end of a Court of Justice of the European Union (ECJ) hearing today in which the world's biggest social network, technology lobbyists and governments faced off against privacy campaigners led by Schrems, who has a record of winning important cases against Facebook.

At issue are standard contractual clauses used by Facebook and other companies to transfer personal data to the United States and other parts of the world and whether these violate Europeans' fundamental right to privacy.

The contractual clauses have been used by numerous companies and other organisations especially since Safe Harbour, the European Union's previous privacy rules, were struck down in a previous case brought by Schrems.

Cross-border transfers worth billions of dollars are a fact of life for businesses ranging from banks to carmakers to industrial giants.

The ECJ Advocate General's opinion will be non-binding but such opinions are influential and usually followed by the court's judges at a later date.

The legal action was referred to the ECJ by the High Court, which has asked it to decide on 11 questions relating to SCCs.

That move followed the taking of a case by Data Protection Commission chief, Helen Dixon, seeking clarity on the issue.

But the origins of the case date back to a complaint made against Facebook to the commission by Mr Schrems in 2013.

He sought to stop transfers of personal data by the social network to the US from the EU, after former US security contractor turned whistle-blower, Edward Snowden, disclosed that the US intelligence services had access to personal data of European technology users under surveillance programs like "PRISM".

In 2015 he won a landmark case that led to the Safe Harbour data transfer agreement between the two territories being ruled invalid.

Mr Schrems was then allowed to amend and resubmit his complaint to the Office of the Data Protection Commissioner focusing on the legality of SCCs.

Ms Dixon then asked the High Court to refer the matter to the European Court of Justice for adjudication.

In October 2017 the High Court gave its judgment in the matter and the following May sent a number of issues to the CJEU.

That decision was appealed to the Supreme Court by Facebook, but the appeal was dismissed in May of this year allowing the European court hearing to proceed.

A judgment is expected to be delivered by the CJEU by the end of the year.