The bulk collection of phone records of Americans by the National Security Agency has been found to likely violate the Fourth Amendment.

Judge Richard Leon ruled Monday that the NSA’s mass collection of “metadata” falls under the Constitution’s prohibitions against unreasonable search and seizure. The ruling in the U.S. District Court for the District of Columbia is viewed as a blow to the Obama administration.

Observers say the case will very likely go all the way to the Supreme Court.

“The government does not cite a single case in which analysis of the NSA’s bulk metadata collection actually stopped an imminent terrorist attack,” Judge Leon wrote in his decision. “Given the limited record before me at this point in the litigation – most notably, the utter lack of evidence that a terrorist attack has ever been prevented because searching the NSA database was faster than other investigative tactics – I have serious doubts about the efficacy of the metadata collection program as a means of conducting time-sensitive investigations in cases involving imminent threats of terrorism.”

The ruling by the judge says the lawsuit brought by a conservative lawyer and the father of a Navy soldier is likely to be successful. The judge did grant a reprieve to the NSA by placing his order to stop the NSA collection efforts on hold until the government can appeal.