An emerging budget deal between Rep. Paul Ryan (R-Wis.) and Sen. Patty Murray (D-Wash.) is hitting some roadblocks Monday, in the form of conservative opposition to its proposed higher spending levels.

Heritage Action became the most significant conservative group to come out and bash the deal, which congressional aides have suggested for more than a week is close.

Some prominent conservative commentators have also been sounding similar notes:

Paul Ryan seems perpetually to come up with deals where his starting point should be the ending point. — Erick Erickson (@EWErickson) December 9, 2013

if Paul Ryan puts his name in a deal that spends more than $1 trillion, his 2016 hopes are over. — Conn Carroll (@conncarroll) December 9, 2013

Here's Heritage Action's full statement:

"Heritage Action cannot support a budget deal that would increase spending in the near-term for promises of woefully inadequate long-term reductions," the organization said in a statement.

"While imperfect, the sequester has proven to be an effective tool in forcing Congress to reduce discretionary spending, and a gimmicky, spend-now-cut-later deal will take our nation in the wrong direction."

Details of the deal remain murky, as both Ryan and Murray keep their cards close to their vests. But the latest reports suggest that the mini-bargain would set discretionary spending levels a little above $1 trillion for the next two years, while repealing and replacing some cuts of sequestration.

The higher discretionary spending levels — spending on programs that have to be reauthorized by Congress every year — are the source of the emerging conservative opposition. Conservatives argue that while imperfect, sequestration has been the only effective check against the Obama administration's spending.

Last week, three conservative members of the House — Mick Mulvaney (S.C.), Jim Jordan (Ohio) and Steve Scalise (La.) sent a letter to House Speaker John Boehner and Majority Leader Eric Cantor urging them to bring a "clean" continuing resolution to the floor that would fund the government at the $967 billion level under sequestration.

As of Thursday, according to Politico, the letter only had 19 signatures. And many Republican defense hawks oppose a "clean" CR, saying that the defense cuts under sequestration are harmful to national security. But the three conservative members spearheading the effort, plus groups like Heritage Action, are the types who wield considerable influence within the House Republican caucus. The Club for Growth, another influential conservative group, did not respond to a request for comment on the deal.

The self-imposed deadline for a budget deal is Friday, though that's a "soft" marker. The government runs out of funding Jan. 15, after which the government would shut down again. Still, the best option for Ryan and Murray is to fast-track the bill through the House before it leaves for holiday recess Friday, and through the Senate before it skips town next week.

The emerging deal also has its Democratic opponents, including those who think that an extension of benefits to the long-term unemployed should be extended.