In a case that could transform the way in which data crosses the Atlantic, Facebook told the European Union’s highest court on Tuesday that EU-U.S. trade would be severely harmed if a data-sharing agreement were ruled illegal.

Arguments have begun at the European Court of Justice in Luxembourg in a case that addresses claims that the U.S. does not sufficiently protect Europeans’ data when it is shipped across the Atlantic. At stake are so-called standard contractual clauses (SCCs) – legal mechanisms that allow companies to move data freely from Europe to the U.S., Asia and other locations.