Max Schrems and his lawyer Herwig Hofmann walk in the hallway at the European Court of Justice in Luxembourg.

Facebook and other Internet giants could be barred from sending European citizens’ personal information to the US after the EU’s top court on Tuesday struck down a key transatlantic data deal in the wake of the Edward Snowden scandal.

The landmark verdict stemmed from a David-and-Goliath case lodged by Max Schrems, an Austrian privacy campaigner, who challenged Irish authorities over user data transferred to the US from Facebook’s European base in Ireland.

“The message is clear — mass surveillance is not possible in Europe (and is) against fundamental rights,” Schrems, who turns 28 this month, told reporters at the European Court of Justice in Luxembourg.

The blow to US firms sets up another transatlantic clash over privacy since the US National Security Agency whistleblower Snowden in 2013 revealed a worldwide surveillance program using user data harvested from Silicon Valley giants.

The court said the “Safe Harbor” agreement that the US and European Commission reached in 2000, on the basis that standards were similar in the US, did not sufficiently guarantee the protection of Europeans’ personal data.

“The Court of Justice declares that the commission’s US Safe Harbor Decision is invalid,” the Luxembourg-based court said in a three-page judgment welcomed by campaigners.

Irish authorities now had to decide whether transfer of data from Facebook’s European subscribers to the United States should be suspended “on the ground that that country does not afford an adequate level of protection of personal data,” the court said.

Ireland’s data protection commissioner said the case would now be considered by the country’s high court “as soon as is practicable.”

Thousands of companies ranging from Google and Amazon to smaller businesses also rely on Safe Harbor to transfer personal data — ranging from names, addresses and dates of birth to anything else they add to their profiles — from Europe to the US.

Facebook called for Washington and Brussels to sort out the situation urgently, while insisting the case was “not about Facebook.”

“It is imperative that EU and US governments ensure that they continue to provide reliable methods for lawful data transfers and resolve any issues relating to national security,” a Facebook spokeswoman said in a statement.

The European Commission was due to hold a press conference at which it was widely expected to announce the imminent agreement of a new version of the Safe Harbor pact with the US.

Commission spokesman Margaritis Schinas said it was an “important decision that raises a number of political issues.”

Schrems had argued that the 15-year-old Safe Harbor deal was too weak to guarantee the privacy of European residents following the revelations by Snowden, but the case was originally rejected by Ireland.

He jubilantly tweeted “Yay!” when the European court ruling came out, hailing it as a “milestone when it comes to online privacy.”

“This decision is a major blow for US global surveillance that heavily relies on private partners,” he said. “The biggest pressure is now on the European Commission and Washington to get to some agreement that functions, because Safe Harbor was for 15 years ago.”

There was no immediate reaction to the judgment from Washington.

But last month the US said an opinion by the EU court’s top legal counsel which reached similar conclusions was based on “inaccurate assertions.”

The EU judgment was welcomed by Germany, where relations with Washington were badly strained when Snowden revealed the alleged tapping of Merkel’s mobile phone by US authorities.

Germany’s justice minister Heiko Maas said the ruling was a “strong signal for fundamental rights protection in Europe,” adding that “those who offer products or services in the EU must adhere to EU data protection rights — no matter where the server is.”

The case also comes amid widespread tensions between Brussels and Washington on issues of regulation, with several EU anti-trust probes currently underway into US tech firms.

Snowden, who remains wanted by the United States and currently lives in Moscow, opened a Twitter account last week, just days before the judgment.