LONDON (AP) — An Austrian privacy campaigner's long-running legal battle against Facebook over its data transfers to the U.S. has reached Europe's highest court.

The European Court of Justice is hearing arguments Tuesday on whether Facebook's Dublin-based subsidiary can legally transfer users' personal data to the U.S. parent company.

The court, based in Luxembourg, is expected to rule on whether "standard contractual clauses" governing data transfers comply with European data protection regulations.

A decision, which is expected by the end of the year, could affect thousands of European Union businesses that rely on the agreements as safeguards to protect personal data sent outside of the bloc.

Privacy campaigner Max Schrems launched the case in 2013 after former NSA contractor Edward Snowden revealed the extent of electronic surveillance by U.S. security agencies.