STRASBOURG, France (AP) — Europe's human rights court is about to publish what could be a landmark ruling on the legality of mass surveillance.

The case brought by civil liberties, human rights and journalism groups and campaigners challenges British surveillance and intelligence-sharing practices revealed by American whistleblower Edward Snowden.

The European Court of Human Rights says the complainants believe that British and U.S. spy agencies may have intercepted their electronic communications.

The court plans to issue its ruling on Thursday morning.

Amnesty International, one of the parties in the case, has previously called it "a major test" for the lawfulness of blanket surveillance. Amnesty lawyer Nick Williams called it "a watershed moment for people's privacy and freedom of expression across the world."