A group of Senate Democrats on Tuesday eased off their push for new Iran sanctions, potentially taking the wind out of the bipartisan effort to muscle through the legislation in the face of a President Obama veto threat. 

In a reversal, Sen. Bob Menendez, D-N.J., announced at a Senate committee hearing that he and his Democratic colleagues had written to Obama telling him they would hold off on supporting legislation that he helped write. The bill was co-authored by Republican Illinois Sen. Mark Kirk. 

"We will not support passage of the Kirk-Menendez bill on the Senate floor until after March 24, and only if there is no political framework agreement," Menendez announced. 

The legislation would tee up new sanctions against Iran if the country fails to strike an acceptable deal curbing its nuclear program. Though the final deadline for those talks is the end of June, March 24 is the soft deadline to reach the outlines of a deal. 

Menendez wants to give the Obama administration until that deadline to see whether the sanctions bill is necessary. His office later released the letter, signed by 10 Senate Democrats including Menendez, saying while they support the bill, they will wait until after March 24 "in acknowledgement of your concern regarding congressional action on legislation at this moment." 

The pushback from Menendez and his colleagues could stall the legislation. 

The Senate banking committee, which held Tuesday's hearing, is still set to consider and vote on the bill on Thursday. Asked for comment on Menendez' announcement, an aide to Kirk said only that the bill would be introduced "shortly" and has "broad bipartisan support." 

But if enough Democrats peel off, it could deprive the 54-seat Republican majority of the 60 votes needed to pass the legislation. At the least, supporters likely would not have the two-thirds majority needed to override a presidential veto. 

The change-up could, for now, end up averting -- or delaying -- a looming veto showdown between Congress and Obama. 

In his State of the Union address, Obama bluntly threatened to veto any bill that could disrupt nuclear talks. 

"New sanctions passed by this Congress, at this moment in time, will all but guarantee that diplomacy fails -- alienating America from its allies; making it harder to maintain sanctions; and ensuring that Iran starts up its nuclear program again," Obama said. "It doesn't make sense." 

On Tuesday, Sen. Sherrod Brown, D-Ohio, urged Congress to hold off, warning of the consequences if lawmakers override a presidential veto. "If Congress acts to force the president's hand in the next few months by overriding his veto and if doing so contributes to the collapse of negotiation and our heading down the path toward a military confrontation, Congress, beginning with each one of us, will be held responsible." 

Sen. Chuck Schumer, D-N.Y., on Tuesday backed Menendez' call to hold off on the bill, while saying he would still vote for it on Thursday so the legislation would be ready to go if needed later on. 

But Republican lawmakers took issue with the administration's argument that passing the bill could derail negotiations. They argued that if Iran walked away from talks over "prospective" sanctions, it shows they weren't serious in the first place. And they reiterated their view that tough sanctions brought Iran to the talks, and it may take the threat of more sanctions to seal the deal. 

"It's clear that sanctions brought Iran to the negotiating table and the threat of future sanctions represent Iran's only incentive to successfully conclude an agreement here," Sen. Richard Shelby, R-Ala., chairman of the banking committee, said Tuesday. 

Menendez said he's "hopeful" diplomacy will prevail in the nuclear talks while noting he's "deeply skeptical" Iran is willing to make the necessary concessions.