The Justice Department warned lawmakers that the National Security Agency will have to wind down its bulk collection of Americans’ phone records by the end of the week if Congress fails to reauthorize the Patriot Act.

Faced with the expiration of the law on June 1 and uncertainty on Capitol Hill, the department circulated a memo on Wednesday that described the powers that will lapse and the actions NSA will have to take in advance to avoid legal challenges.

Congress must deal with the law’s fate before lawmakers leave town for the weeklong Memorial Day recess. The issue has divided Republicans and Democrats, cutting across party lines and pitting civil libertarians concerned about privacy against more hawkish lawmakers fearful about losing tools to combat terrorism.

“After May 22, 2015, the National Security Agency will need to begin taking steps to wind down the bulk telephone metadata program in anticipation of a possible sunset in order to ensure that it does not engage in any unauthorized collection or use of the metadata,” the Justice Department said.

Last week, the House backed the USA Freedom Act, which would replace bulk collection with a system to search the data held by telephone companies on a case-by-case basis. The vote was 338-88, and House Republican and Democratic leaders have insisted on their bill.

But Senate Majority Leader Mitch McConnell, R-Ky., and several other top Republicans prefer to simply reauthorize the post-Sept. 11 law. McConnell has agreed to allow a vote on the House bill, but has indicated that there may not be enough votes to pass it in the Senate.

If Congress fails to act, several key provisions of the law would expire, including the bulk collection; a provision allowing so-called roving wiretaps, which the FBI uses for criminals who frequently switch cellphones; and a third that makes it easier to obtain a warrant to target a “lone wolf” terror suspect who has no provable links to a terrorist organization.

The Justice Department said if Congress allows the law to expire and then passes legislation to reauthorize it when lawmakers return to Washington the week of June 1 it would “be effective in making the authorities operative again, but may expose the government to some litigation risk in the event of legal challenge.”

The White House backs the House bill and has pressed for the Senate to approve the legislation and send it to President Barack Obama for his signature.

The House bill is the result of outrage among Republicans and Democrats after former NSA contractor Edward Snowden’s revelations about the NSA program.

The Republican divisions over the issue was on stark display in the Senate on Wednesday as Sen. Rand Paul, R-Ky., a candidate for president, stood on the floor and spoke at length about his opposition to NSA spying.

(AP)