Facebook has presented a long list of procedural objections to an Austrian court trying to halt a class action lawsuit for 25,000 users that accuses the social media giant of violating their privacy.
The first day of hearings began with a four-hour session in which Facebook's lawyers tried to convince the judge not to admit the suit brought by law student Max Schrems.
The 27-year-old is claiming €500 in damages for each user.
The suit is the latest of several legal challenges in Europe and the United States to Facebook for the way it shares users' personal data with businesses or governments.
Mr Schrems has said this may become a test case for European data protection laws.
"The lawsuit is inadmissible on the procedural level – the court is not responsible," Facebook's lawyer Nikolaus Pitkowitz told the judge.
"It is unjustified in terms of content."
Mr Schrems accused Facebook of engaging in delaying tactics.
"This is a typical strategy, because most consumers will run out of time and money," he said.
The judge said a written decision on whether the court can handle the suit will come before the summer.
In the first hearing, attorneys for Mr Schrems and Facebook battled on technical grounds about whether the student has the status of a private Facebook consumer and if the 25,000 plaintiffs are legally allowed to confer their rights on him.
Mr Schrems is claiming damages for alleged data violations by Facebook, including by aiding the US National Security Agency in running its PRISM programme, which mined the personal data of Facebook users.
"I think we can heighten data protection with this lawsuit," Mr Schrems' lawyer Wolfram Proksch told reporters after the session.
Facebook's lawyers did not address the details of the privacy concerns mentioned in his suit and declined to comment further outside of the court room.
A specialist financier will bear the legal costs if Mr Schrems loses the case and will take 20% of the damages if he wins, meaning users can join the case at no financial risk.