Forty-three GOP senators on Saturday signed a letter addressed to Senate Majority Leader Harry ReidHarry Mason ReidSenate Republicans signal openness to working with Biden Mellman: The likely voter sham Bottom line MORE (D-Nev.) expressing opposition to his debt-ceiling legislation currently being considered in the upper chamber.

Their unified opposition to the bill leaves Democrats at least three votes short of the 60 needed to a clear cloture and virtually assures its defeat when it comes up for a vote tonight or tomorrow morning.

Only moderate Republican Sens. Susan CollinsSusan Margaret CollinsThe Hill's Campaign Report: Biden asks if public can trust vaccine from Trump ahead of Election Day | Oklahoma health officials raised red flags before Trump rally Gideon leads Collins by 12 points in Maine Senate race: poll Senate leaders quash talk of rank-and-file COVID-19 deal MORE (Maine), Olympia Snowe (Maine), Scott Brown (Mass.) and Lisa MurkowskiLisa Ann MurkowskiGOP ramps up attacks on Democrats over talk of nixing filibuster OVERNIGHT ENERGY: House Democrats tee up vote on climate-focused energy bill next week | EPA reappoints controversial leader to air quality advisory committee | Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' House Democrats tee up vote on climate-focused energy bill next week MORE (Alaska) did not sign on to the letter.

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"We are writing to let you know that we will not vote for your $2.4 trillion debt limit amendment which, if enacted, would result in the single largest debt ceiling increase in the history of the United States," reads the letter.

Senate Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellMcConnell focuses on confirming judicial nominees with COVID-19 talks stalled McConnell accuses Democrats of sowing division by 'downplaying progress' on election security Warren, Schumer introduce plan for next president to cancel ,000 in student debt MORE (R-Ky.) took to the floor moments after the letter was delivered to assure Reid, who was also on the floor, that the proposal had no chance of clearing the chamber.

"It’s not going anywhere," said McConnell. "It will not pass the Senate. It will not pass House."

McConnell also accused Reid of "delaying the inevitable" defeat of the bill and called for an immediate vote. The first procedural vote is currently expected at around 1 a.m. on Sunday. 

Reid responded to the news of the letter, which he apparently received while he was on the floor, by asking McConnell what Republicans would agree to since they oppose his plan.

"What will they vote for?" asked Reid. "Do they have any ideas? Let me know.”

The Reid plan would have President Obama request a $2.4 trillion debt-limit increase in two installments of $1.2 trillion each. The requests would be subject to congressional resolutions of disapproval.