The U.S. has backed Facebook in its battle against the European Union, accusing Europe's top court of making "inaccurate assertions" about America's intelligence services.

The U.S. mission to the European Union slammed the court for questioning a crucial data sharing agreement between the U.S. and E.U.

The deal, called "Safe Harbor Framework," makes it possible for thousands of U.S. companies, including tech giants such as Google (GOOGL), Facebook (FB), and Amazon (AMZN), to transfer private data from the E.U. to their servers in the U.S.

But the top legal adviser to European Court of Justice suggested the deal is no longer valid because of allegations of "mass, indiscriminate surveillance" by U.S. intelligence services. The U.S. hit back Monday, saying the claims are "simply not the case."

The court's opinion is part of an ongoing case against Facebook, which was brought by Austrian law student Max Schrems. He said he was uncomfortable with the way Facebook transfers his personal data to the U.S., where it can be accessed by authorities with little respect for his privacy. Schrems was prompted to file his case by revelations in the case of Wikileaks whistleblower Edward Snowden.

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The court's advocate general agreed with Schrems, saying the easy access that U.S. authorities have to the data "constitutes an interference with the right to respect for private life and the right to protection of personal data."

The allegation has made U.S. officials in Brussels angry. "The Advocate General's opinion rests on numerous inaccurate assertions about intelligence practices of the United States," the mission said in the unusually strongly-worded statement.

The court will deliver its final ruling next Tuesday. While the advocate general's opinion is not binding, the court usually follows it.