President Trump, Vice President Pence, and House Speaker Ryan. Getty Images/Pool

House Republican leadership's rollout of a plan to repeal and replace the Affordable Care Act (ACA) was met with sharp resistance Tuesday from conservative lawmakers and influential conservative-leaning groups, putting the future of the legislation in immediate doubt even as President Donald Trump's administration signaled approval.

Hard-line conservatives who have vowed to fully repeal Obamacare voiced concerns with the GOP's attempt to repeal and replace it, signaling they feel it doesn't go far enough.

Rep. Mark Meadows, head of the influential conservative House Freedom Caucus, told Fox News' Sean Hannity that the AHCA "sets a new entitlement, keeps some taxes, doesn’t repeal all of Obamacare."

"We’ve got to do better, and hopefully with some new amendments we can do that," Meadows said.

In the same interview with Hannity, Rep. Louie Gohmert, a conservative firebrand who is not a part of the House Freedom Caucus, criticized the bill and said he had already heard concerns from constituents.

The House Freedom Caucus is expected to hold a press conference at 3:30 p.m. ET to lodge complaints about the bill. If all Democrats vote their party line, the House GOP could not afford to lose the Freedom Caucus membership.

And the Republican Study Committee — a conservative caucus with 172 members — released a memo criticizing the AHCA as well, specifically the tax credits proposed for people to buy healthcare if they do not receive it from their employer or a government program like Medicare or Medicaid.

"Writing checks to individuals to purchase insurance is, in principle, Obamacare," said the memo, which went on to criticize the cost of the credits.

The RSC memo also attacked the fact that the new bill will allow the ACA's Medicaid expansion to last until 2020, saying it will continue to "contribute to the worsening of the federal and state budgets."

Other Congressional Republicans were more aggressive in their criticisms of the legislation, which has been spearheaded by the heads of the House Ways and Means and House Energy and Commerce committees with the support of top leaders like House Speaker Paul Ryan. Rep. Justin Amash, a longtime critic of Obamacare and House Freedom Caucus member, tweeted that the AHCA was "Obamacare 2.0."

And Sen. Rand Paul — who has been railing against the House plan since a draft of the bill was leaked — tweeted on Tuesday that he did not support the House GOP plan.

"House leadership plan is Obamacare Lite," Paul tweeted. "It will not pass. Conservatives are not going to take it."

GOP Sen. Roy Blunt of Missouri told a local radio station that the bill may not get enough votes to make it past the Senate, according to CNN's K-File.

"What I don't like is it may not be a plan that gets a majority votes and let's us move on," said Blunt. "Because, we can't stay where we are with the plan we've got now."

Sen. Mike Lee of Utah, who came out against the leaked draft bill along with Paul and Sen. Ted Cruz, also released a press release criticizing the Hose GOP bill.

"This is not the Obamacare repeal bill we’ve been waiting for," said Lee. "It is a missed opportunity and a step in the wrong direction."

Key conservative-leaning advocacy groups also came out skeptical of the bill. Heritage Action of America, the advocacy arm of the influential conservative Heritage Foundation think tank, also came out against the AHCA in a statement on Tuesday.

"Many Americans seeking health insurance on the individual market will notice no significant difference between the Affordable Care Act (i.e., Obamacare) and the American Health Care Act," said the statement from Heritage Action CEO Michael Needham. "That is bad politics and, more importantly, bad policy."

Other conservative groups, including Club for Growth, Freedom Partners, and Americans for Prosperity have also come out against the bill. Club for Growth even dubbed the plan "Ryancare," a nod to the House speaker.

Michael Cannon, the director of conservative think tank Cato Institute's health policy studies, also attacked the bill in a column on Tuesday calling it "a train wreck waiting to happen" and saying it does not repeal enough of the ACA.

"Obamacare would consume the rest of Congress’ and President Trump’s agenda," wrote Cannon. "Delaying or dooming other priorities like tax reform, infrastructure spending, and Gorsuch. The fallout could dog Republicans all the way into 2018 and 2020, when it could lead to a Democratic wave election like the one we saw in 2008."

In an interview with "Fox and Friends," Paul also criticized a provision in the AHCA that allows insurance companies to charge people who do not maintain continuous health-coverage premiums up to 30% more than if they had kept coverage. Paul said that instead of Obamacare's individual mandate, in which a consumer who does maintain coverage pays the government a penalty, this provision would amount to a mandate that benefited insurers and is "likely unconstitutional."

"So much of their bill is a bail out for the insurance companies," Paul said.

On the other end, four GOP senators wrote a letter before the release of the House GOP's bill, saying they would not support the leaked draft of the bill because of its inadequate protections of the ACA's Medicaid expansion. The expansion has allowed 11 million people to access health insurance and has become popular in states that have expanded coverage.

While these senators have not commented on the new bill yet, the AHCA does not make many major changes to the leaked memo's Medicaid expansion phase-out, which would end the current federal funding program in 2020 and shift funding to a per-capita program in 2020 that experts say would most likely be less generous.