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 ReidBill O'Reilly: Politics helped kill Kate Steinle, Zarate just pulled the trigger Tax reform is nightmare Déjà vu for Puerto Rico Ex-Obama and Reid staffers: McConnell would pretend to be busy to avoid meeting with Obama MORE (D-Nev.) promised a vote on those provisions as an amendment.

A group of GOP senators, led by Sens. Mike LeeMichael (Mike) Shumway LeeSupreme Court takes on same-sex wedding cake case House approves motion to go to tax conference — with drama Trump really will shrink government, starting with national monuments MORE (Utah), Rand PaulRandal (Rand) Howard PaulLexington mayor launches bid for Congress Trump-free Kennedy Center Honors avoids politics Meet the Iran hawk who could be Trump's next secretary of State MORE (Ky.) and Ted CruzRafael (Ted) Edward CruzDebbie Wasserman Schultz marks 10 years as breast cancer survivor Foreign agent registration is no magical shield against Russian propaganda Let Trump be Trump and he'll sail through 2020 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 ManchinJoseph (Joe) ManchinTrump rips Dems a day ahead of key White House meeting Senate panel moves forward with bill to roll back Dodd-Frank Wealthy outsiders threaten to shake up GOP Senate primaries 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.