By Ashley Killough, CNN

updated 8:52 AM EST, Fri November 14, 2014

STORY HIGHLIGHTS

(CNN) -- Sen. Rand Paul, a fierce critic of the National Security Agency's domestic surveillance programs, will oppose the NSA reform bill in the Senate in large part because it includes an extension of the Patriot Act, a senior Paul aide said Friday.

Known as the USA Freedom Act and proposed by Sen. Patrick Leahy, D-Vermont, the bill bans bulk collection of Americans' phone records by placing narrower limitations on government searches.

Read the bill's text | Supporters

The legislation also extends the Patriot Act's sunset from June 2015 to December 2017.

The Senate will vote probably next Tuesday whether to take up and begin debate on the bill. It's unclear if they'll have the votes to move forward, but with Paul's opposition, it will make it that much tougher to clear that procedural hurdle.

Paul "strongly favors reforming the NSA" and while he may have been expected to support the current bill, a senior aide said the Kentucky Republican won't back the legislation.

"Due to significant problems with the bill, at this point he will oppose the Leahy bill," the aide told CNN. The aide pointed out the extension of the Patriot Act as a key issue, but declined to name other "significant problems."

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