The Senate is trying to start work on S. 649, the Safe Communities, Safe Schools Act, which would expand background checks on gun purchases, create new penalties on straw purchases and include new funding for school security. The bill doesn’t include an assault weapons ban or limits on magazine clip capacity — although Senate Majority Leader Harry ReidHarry ReidWarren cautions Dems against infighting Dems see surge of new candidates Dems to grind Senate to a halt over ObamaCare repeal fight MORE (D-Nev.) promised a vote on those provisions as an amendment.

A group of GOP senators, led by Sens. Mike LeeMike LeeGOP at decisive moment on Planned Parenthood Trump: ‘I cannot imagine’ GOP senators don’t back healthcare bill Trump called Cruz to press him on ObamaCare repeal bill: report MORE (Utah), Rand PaulRand PaulGOP at decisive moment on Planned Parenthood Trump: ‘I cannot imagine’ GOP senators don’t back healthcare bill Sunday shows preview: Senate healthcare debate heats up MORE (Ky.) and Ted CruzTed CruzGOP at decisive moment on Planned Parenthood Trump: ‘I cannot imagine’ GOP senators don’t back healthcare bill Trump making calls to senators on healthcare bill MORE (Texas), has threatened to filibuster any gun control reforms because they say it would violate Second Amendment rights.

Earlier Thursday, the Senate voted 68-31 for cloture on the motion to proceed. Sixteen Republicans supported moving forward with the bill. Unless a unanimous consent agreement to vote on the motion to proceed is reached sooner, the Senate won’t be able to hold that vote until Friday afternoon at the earliest.

The aide said GOP senators could also force the Senate to spend four days on each amendment vote by objecting to unanimous consent agreements and requiring cloture votes throughout the process. If cloture were filed on an amendment on Monday, the vote to end debate would be Wednesday, and if cloture were invoked, the Senate would have to wait another 30 hours before finally voting on the amendment.

Reid said he wanted to have an open amendment process on the gun control reform package, but that he would need the cooperation of Republicans, by not filibustering each amendment.

Reid said that the first amendment considered would be a new deal on background checks from Sens. Joe ManchinJoe ManchinSunday shows preview: Senate healthcare debate heats up Zinke hits Dems for delaying Interior nominees Manchin faces primary challenge from the left MORE (D-W.Va.) and Pat Toomey (R-Pa.).

Republicans expressed concern that extending background checks could create a federal registry of gun owners and make it harder for family members to transfer firearms. Lee complained that senators hadn’t been given enough time to read through Manchin and Toomey’s plan.

"Yesterday Sens. Toomey and Manchin announced a new proposal, yet as of this very moment not a single senator has been provided the text of that provision," Lee said Thursday. "It’s critical that we all know what’s in the bill before we vote on it. ... Proponents of this bill say the people deserve a vote, but don’t they also deserve to know what they’re voting on? I think they do.”

Manchin and Toomey’s deal would expand background checks to cover all sales at gun shows and over the Internet. Those background checks would have to be accompanied by records proving to law enforcement officials they took place. It would exempt gun sales and transfers between friends and acquaintances and explicitly bans the federal government from creating a national firearms registry.