Republicans in US Congress released a long awaited plan for the replacement of the Affordable Care Act (ACA), also know as Obamacare — the flagship health act of the last White House administration which saw millions gain health coverage.

The GOP ran on a platform of repealing and replacing the ACA and Monday night (6 March) provided the first real glimpse of what that replacement would be.

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The new healthcare bill reportedly keeps popular elements of the Obama administration's plan - including provisions allowing children to stay on their parents insurance until they are 26 and ensuring that insurers cannot deny coverage to people with pre-existing medical conditions.

But, in more conservative measures, the Washington Post reported that the legislation takes aim at Planned Parenthood, a bête noire of anti-abortion groups.

Under the new plan proposals, the organisation would be ineligible for federal family planning grants and Medicaid reimbursements. The new act would also give tax credits as an incentive for Americans to buy health insurance, rather than the current system of mandatory coverage with federal subsidies.

Despite Republicans holding a majority in both the House of Representatives and the Senate, misgivings from different wings of the party threaten to scupper the bill in the upper chamber. Four Republican Senators, Rob Portman of Ohio, Shelley Capito of West Virginia, Cory Gardner of Colorado and Lisa Murkowski of Alaska, all signed a letter addressed to Majority Leader Mitch McConnell saying they were "concerned" that a February draft of the proposal "does not provide stability and certainty for individuals and families in Medicaid expansion programs or the necessary flexibility of states."

All four Senators represent states that expanded Medicaid coverage under the ACA.

"We are concerned that any poorly implemented or poorly timed change in the current funding structure in Medicaid could result in a reduction in access to life-saving health care services." the letter read.

"We believe Medicaid needs to be reformed, but reform should not come at the cost of disruption in access to health care for our country's most vulnerable and sickest individuals ... we will not support a plan that does not include stability for Medicaid expansion populations or flexibility for states," it added.

Kentucky Senator Rand Paul, who went on a congressional treasure hunt last week in protest at the secrecy around the replacement bill, tweeted earlier on Monday that he still had not seen the bill but "from media reports this sure looks like Obamacare Lite!"