WASHINGTON –

, on Monday blocked quick passage of controversial intelligence bill amid concerns that it gives the government too much power to secretly collect data on U.S. citizens.

Wyden’s decision to place a “hold” on a bill that would extend the Foreign Intelligence Surveillance Act for five years is just the latest installment in his

over the

Wyden has sought details for months on the number of Americans whose data has been collected as part of surveillance of foreign citizens who are or interest to intelligence officials. The government has yet to provide an answer that satisfies Wyden.

The second concern is that a U.S. citizen could have his or her personal information and communication analyzed as a by-product of an operation directed at a foreign citizen. Wyden is demanding that the government first obtain a warrant to review the information about the U.S citizen. Current law considers that additional information to be covered by the original warrant giving permission to monitor a foreign citizen, a practice Wyden condemns as a “backdoor” search.

“I am concerned, of course, that if no one has even estimated how many Americans have had their communications collected under the (law),” Wyden said in a statement announcing his decision to block the bill.

“Then it is possible that this number could be quite large. Since all of the communications collected by the government … are collected without individual warrants, I believe that there should be clear rules prohibiting the government from searching through these communications in an effort to find the phone calls or emails of a particular American, unless the government has obtained a warrant or emergency authorization permitting surveillance of that American,” he wrote.

Wyden’s singular act carries power in the Senate, where rules require “unanimous consent” for such routine acts as bringing a bill to the floor. A single objection – or hold – by a senator is sufficient to derail all progress until the concerns are resolved. The Senate's Democratic leadership has not said when the bill would come to the floor but there is pressure to move quickly. The current law expires at the end of the year.

While Wyden’s blockade was an individual act, he is not alone.

, D-Colo., expressed similar concerns on Friday. He and Wyden have joined forces in the past on the issue.

“The FISA Amendments Act has yielded important intelligence and should be continued, but we need more information about its impact so that Congress can consider whether privacy protections should be clarified or strengthened,” Udall said. “I also believe we need to put in place new protections against warrantless searches for Americans' communications."

Supporters in Congress and the administration say there are sufficient safeguards even if they aren’t full disclosed. The law allows the government to sweep up vast amounts of phone, email and other types of communication of non-citizens deemed to threats. It also requires the government to obtain a warrant to collect communications data on U.S. citizens.

The law is the target of a court suit brought by the American Civil Liberties Union and other groups that maintain that the measure gives the National Security Agency almost unchecked power to monitor Americans' international phone calls and emails.

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