Updated

The National Security Agency has begun winding down its collection and storage of American phone records after the Senate failed to agree on a path forward to change or extend the once-secret program ahead of its expiration at the end of the month.

Barring an 11th hour compromise when the Senate returns to session May 31, a much-debated provision of the Patriot Act and some other lesser known surveillance tools will sunset at midnight that day.

The change also would have a major impact on the FBI, which uses the Patriot Act and the other provisions to gather records in investigations of suspected spies and terrorists.

The move comes after Senate Republicans blocked a House-passed measure supported by the president.