House Republicans are still struggling to reach consensus on a plan to fund the government, with lawmakers going back-and-forth over the issue during a closed-door party meeting on Tuesday morning.

GOP leaders are planning to plow ahead with a vote on their proposal this week, even as some conservative hardliners are still digging in and threatening to oppose a procedural vote, which would prevent the bill from coming to the floor. GOP lawmakers stood up during the meeting to make their case for -- or against -- the plan, which would temporarily fund the government and beef up border security but is dead-on-arrival in the Democratically-controlled Senate.

House GOP leaders canceled a procedural rule vote on the proposal originally slated for Tuesday amid that opposition from hardliners. It's unclear when or if that vote will get rescheduled.

"There are a lot of 'No' votes in that room. I don't know how they will get to 218," said Rep. Nancy Mace, a South Carolina Republican, exiting the meeting. "Without a deal with Democrats, I don't see it passing. ... It is going to be a long two weeks."

Government funding is slated to run out on September 30.

House Speaker Kevin McCarthy encouraged members who are opposed to the idea to work out their difference in House GOP Whip Tom Emmer's office, according to sources in the room.

And Rep. Scott Perry, a conservative Republican from Pennsylvania and the chairman of the House Freedom Caucus who helped negotiate the deal, told members during the meeting that if they are opposed to the current plan but think there's something else that might support, "please tell someone what that is," sources said.

Some conservative hardliners are now floating the idea of amending the proposal to include lower spending cuts. Republican Rep. Bob Good of Virginia said leadership is "entertaining everything" at this point, and said that even though the deal was negotiated by some members of the Freedom Caucus, he made clear they were not representing the entire group.

But he also predicted it would be hard to avoid a government shutdown at this point, though he added, it should not be something that they "fear."

Rep. Ralph Norman, a South Carolina Republican, said he thinks they should work through the weekend until they are able to find agreement among House Republicans on how to keep the government open. He said he accidentally voted to support a rule for the short-term funding bill, saying he was "asleep at the wheel" during the meeting on Monday night, but plans to vote against the rule when it comes to the floor.

Rep. Chip Roy, a Texas Republican and one of the negotiators of the package, suggested that one of the potential ways to move forward would be for the speaker to lay out a topline spending number and spending numbers for each of the appropriations bills to help members who are still on the fence see the full picture.

"I think the biggest thing that I have heard -- and this is where my colleagues I think have a really important point -- what do we do next? The speaker needs to set a topline, needs to set a structure, a target," Roy said. "I have been saying that for months. We are here in my opinion because we haven't had a clear target."

But Roy did blast some of the opposition.

"I find it extremely difficult to explain or defend opposition to an 8% cut over 30 days in exchange for the most conservative and strong border security measures we've ever passed out of this body," he said. "I think that is inexplicable. I think it is malpractice, and I think there are some outside groups ... who are trying to advance themselves that are a part of this that are pushing this narrative that it is somehow malpractice to do that when what would be true malpractice is to head into a shutdown without a coordinated and concerted message."

Florida GOP Rep. Byron Donalds said that members who negotiated the bill are willing to talk.

"I want to get real conservative wins, not talking points, not tweets, not any of that stuff," Donalds said.

Perry said he continues to try and sell the bill to his colleagues and his message is simple, they can keep making changes but at some point, they have to decide: Do they want to pass something or get jammed by the Senate?

"This is a proposal. I speak for myself. It doesn't mean that I love it, but I am working with my colleague to secure one of two paths. The one path is where we offer something and the American people can see what we stand for, the other path is quite honestly accepting whatever the Senate sends us," Perry said. "You are not going to get every single thing that you want, but if you don't do something, you aren't going to get anything."

There are at least 15 members currently opposed, and more that are undecided, according to an CNN whip count. Among those who are opposed: Reps. Good, Norman, Andy Ogles of Tennessee, Matt Gaetz of Florida, Dan Bishop of North Carolina, Andy Biggs of Arizona, Tim Burchett of Tennessee, Anna Paulina Luna of Florida, Marjorie Taylor Greene of Georgia, Matt Rosendale of Montana, Victoria Spartz of Indiana, Eli Crane of Arizona, Cory Mills of Florida, Wesley Hunt of Texas and Paul Gosar of Arizona.

Those 15 "No" votes would easily sink the bill without any Democratic support, as Republicans control 221 seats to Democrats' 212.

House Rules Committee Chair Tom Cole of Oklahoma had told reporters he planned to go to the floor Tuesday with the rule, but House leaders later pulled a procedural rule vote on their short-term spending bill later Tuesday morning, in another sign that House Republicans are deeply divided on the path forward.

Even if his own party sinks the bill, Cole said he is not worried about the overall strategy.

"Welcome to politics," Cole told reporters.

Cole, who said some of the "No" votes are "movable," warned his colleagues who are withholding their votes for the wrong reasons.

"That's not good legislation and that's blackmail," he said.

This story has been updated with additional developments.