Conservatives in Congress are casting stern glares at an GOP Obamacare replacement plan released Monday, spelling trouble for an effort that's already on shaky footing.

The Republican Study Committee, a group of 150-plus conservative House members, sent out a memo Monday night raising serious concerns with the bill, which would roll back major parts of the healthcare law, but not as quickly or as fully as many members would prefer.

The RSC memo lists a litany of "concerns" with the legislation, calling its tax credits a "Republican welfare entitlement." Concerns include the bill's maintenance of Medicaid expansion for three years and its reliance on government spending through tax credits to ensure poor Americans get coverage.

The memo raises doubts that Congress would be able to pay for the tax credits without deficit spending or raising taxes and predicts that Medicaid expansion would likely never be repealed due to political reasons.

"The major cause for the delay is to avoid the political consequences and pain of unwinding expansion, especially in Republican-held states with upcoming gubernatorial contests," the memo says. "It is unlikely that the expansion repeal will ever be implemented in reality."

Members of the Freedom Caucus—and their allies in the Senate—were even more explicit in condeming the Obamacare replacement that leadership is trying to advance through Congress.

Rep. Justin Amash, a Michigan Republican known as one of the Freedom Caucus's more rowdy members, tweeted that it was "Obamacare 2.0." Kentucky Sen. Rand Paul, who has his own replacement plan, dubbed the measure "Obamacare lite." Paul and Freedom Caucus Chairman Mark Meadows had published an op-ed earlier in the day calling for a quick vote on repealing the healthcare law, before starting the debate on how to replace it.

Conservatives have been getting impatient for a vote to repeal the law, as they'd promised voters for years that they'd get rid of it, given the chance. They have that chance, now that President Trump is in office, but the GOP has found it hard to rally around a plan.

Conservatives had already indicated they don't like the idea of refundable tax credits—included in the plan released Monday — and are likely to be disappointed the measure doesn't phase out the law's Medicaid expansion until 2020.

Two key House committees – Ways and Means and Energy and Commerce – plan to mark up the legislation starting this week. House Speaker Paul Ryan has insisted he wants to move the bill through regular order.

But Ryan and other GOP leaders are facing pressure from all sides. Democrats are deeply opposed to repealing the law at all, with House Minority Leader Nancy Pelosi saying Monday that it would merely cost people their coverage. Conservatives, already annoyed that it's taken this long to get a replacement bill, want to do away with as much of the law as possible. And some Senate moderates have aired competing concerns about chipping away at Americans' Medicaid coverage.

Some conservatives held their fire Monday evening, saying they needed more time to review the measure. Mark Walker, chairman of the House Republican Study Committee, pointed to a few areas he's concerned about—whether the measure includes adequate abortion restrictions, whether it eliminates Medicaid expansion and whether its insurance subsidies aren't too expensive.

"I applaud the movement and believe it is the right direction," Walker said in a statement provided to the Washington Examiner. "We are carefully reviewing this legislation looking in three main areas of shared conservative concern: protection of the unborn, elimination of Obamacare's Medicaid expansion and ensuring the tax credits are fiscally responsible."

Heritage Action spokesman Dan Holler, who has also pushed for a quick repeal vote, said Heritage will take a close look at the plan but didn't initially cast judgment.

"Conservatives have raised valid concerns about previous drafts," Holler tweeted.