Washington (CNN) – Four Republican senators who were on the fence about a bipartisan compromise on gun control said on Monday they would now oppose the measure.
Sens. Saxby Chambliss of Georgia, Roger Wicker of Mississippi, and Richard Burr of North Carolina told CNN of their plans regarding the deal struck by Sens. Pat Toomey, R-Pennsylvania, and Joe Manchin, D-West Virginia, to expand background checks to private transactions at gun shows and in online sales.
Sen. Jeff Flake of Arizona announced his decision on his Facebook page.
“(The agreement) would expand background checks far beyond commercial sales to include almost all private transfers – including between friends and neighbors – if the posting or display of the ad for a firearm was made public. It would likely even extend to message boards, like the one in an office kitchen. This simply goes too far,” Flake wrote.
The Senate is expected to take up a package of gun proposals this week, starting with the Manchin-Toomey amendment. The overall gun package also contains measures to crack down on gun trafficking and straw purchases, and finding ways to improve school safety.
Earlier in the day, Manchin told CNN a vote on his amendment would be pushed back to try and build more support in order to get the 60 votes that are effectively needed for passage.
Asked if the vote would take place Tuesday or Wednesday, as supporters had hoped, Manchin said he didn't think so.
"I would say by the end of the week, probably," he added.
Four Republicans have voiced support or said they were leaning in favor of supporting the amendment. With at least two moderate Democrats from pro-gun states known to oppose the measure, it needs at least seven GOP votes to have any chance of passing.
Flake said he supports background checks but believes the current system need to be strengthened.
He mentioned a bill he’s co-sponsoring with Sen. Lindsey Graham, R-South Carolina, Sen. Mark Begich, D-Alaska, and Sen. Mark Pryor, D-Arkansas, that will focus on “clarifying who should not be able to obtain a firearm due to mental illness.”
Flake said he believes their approach is “preferable, and more workable” than mental health provisions in the Manchin-Toomney plan.
“I will oppose the Manchin-Toomey amendment,” he wrote.
Separately, gun control proponents postponed an initiative scheduled for Tuesday due to the bombing in Boston. The coordinated event, run by the advocacy group Organizing for Action, would have organized supporters to call their senators and urge them to support the current gun legislation.
– CNN’s Tom Cohen and Ashley Killough contributed to this report.