Senate Republicans are signaling they’re not going to agree to move forward on a scaled-down bipartisan infrastructure package if Senate Majority Leader Charles Schumer (D-N.Y.) goes ahead with his plan to force a vote Wednesday.

Schumer has said the Senate will vote Wednesday to begin debate, but GOP aides on Monday say Republicans will withhold their support, preventing the Senate from getting the 60 votes necessary to trigger debate on the $1.2 trillion, eight-year bipartisan proposal. 

Democrats are worried that Republicans are seeking to run out the clock on talks on the bill, making it more difficult for Democrats to pass a separate $3.5 trillion package that is connected to the talks. 

But Republicans say the bipartisan bill has yet to be written and Schumer is rushing the process. 

Senate Minority Leader Mitch McConnell (R-Ky.) on Monday said that Republicans will not vote to proceed to the infrastructure bill until the bipartisan negotiators reach a final agreement and release the legislative text.

“We need to see the bill before voting to go to it. I think that’s pretty easily understood,” he told reporters after walking off the Senate floor.

Pressed again on whether his caucus would vote to defeat a motion to begin debate, McConnell repeated: “I think we need to see the bill before we decide whether or not to vote for it.”

Sen. Susan Collins (R-Maine), a key member of the bipartisan group, said Monday that work to finalize the bill won’t likely be finished by Wednesday. Collins told a reporter that Schumer should call off Wednesday's procedural vote because the bipartisan group won’t be able to wrap up its work in the next two days.  

Democrats are pointing out that Republicans have been willing to begin debates before even if legislation is still being crafted.

Thirty-seven Republicans voted to proceed to the Endless Frontier Act, legislation the Senate passed last month to improve U.S. competitiveness with China, on May 17 even though major components had yet to be added through a substitute amendment.

But Republican aides say the bipartisan infrastructure package is a much more significant bill.

One GOP aide said Schumer’s decision to force the procedural vote Wednesday “has pissed people off” and is “forcing the issue before it’s ready.”

“This is something that’s far more substantial than that,” the aide said of the bipartisan infrastructure bill compared to the motion to proceed to the Endless Frontier Act in the spring.

The aide said Republican senators are not expected to vote to begin the debate the bill “if they’re still working on it.”

Aides said there would be a more complete picture of what to expect after Senate Republican leaders hold their weekly meeting Monday afternoon and other lawmakers have time to speak face-to-face on the Senate floor.

The latest holdup is a dispute over a proposal to provide $40 billion to the Internal Revenue Service to beef up enforcement of tax compliance, which was estimated to net $100 billion in revenue to help offset the cost of infrastructure spending.

Conservative Republicans rebelled against the idea in recent weeks, putting pressure on moderate GOP senators in the bipartisan group to back off from it.

It now looks like that proposed way to pay for it will be pulled from the bill, but that leaves negotiators in the tough position of finding $100 billion from another revenue source. Another option would be to shrink the overall cost of the bill, which is estimated at $1.2 trillion over eight years or $973 billion over five years.

Republican negotiators signaled over the weekend they’re not ready to vote on beginning the Senate debate Wednesday, even though there are only three weeks left in the work period before the August recess, which is scheduled to begin Aug. 6.

Sen. Rob Portman (Ohio), the lead Republican negotiator, says the bipartisan group is working on the “final details” and has pushed back against what he’s called Schumer’s “arbitrary deadline.”

“We’ll push as hard as we can. We’re working all weekend again and that’s important. It’s important we get it done because it’s an urgent matter. But we ought not to have an arbitrary deadline forcing this process,” Portman said on CNN’s “State of the Union” on Sunday.

Schumer is pressing the bipartisan group to agree to move forward this week on the $1.2 trillion infrastructure proposal because he wants the Senate to also take up and pass the budget resolution before Congress leaves town for an extended recess.

Another key negotiator, Sen. Bill Cassidy (R-La.), said Sunday that he would not vote to proceed to a House-passed shell bill that would be used to pass a bipartisan infrastructure deal through the Senate if the bipartisan negotiators haven’t finalized their agreement.

“How can I vote for cloture when the bill isn’t written?” Cassidy asked on “Fox News Sunday” with Chris Wallace.

Cassidy also said he and his colleagues need a “little bit more time to get it right.”

The Louisiana senator complained that the Senate leadership and the White House haven’t been willing to make enough concessions to help the process along.

“We need Senate leadership, Schumer and the White House to work with us. Right now I can frankly tell you that they’ve not,” Cassidy said on Fox. “We are competing with their $3.5 trillion plan. They want everything reasonable on their side, not helping us. Again, we can pass this, we just don’t need programmed failure.”

--Updated at 3:42 p.m.