Democrats are accusing Republicans of trying to rush a “shameful” bill meant to repeal and replace Obamacare through the Senate “in the dark of the night” without allowing enough time for debate or to make changes.

Speaking on the Senate floor, Senate Democratic leader Chuck Schumer slammed Majority Leader Mitch McConnell for not allowing Democrats more than “10 hours of debate on a bill that affects one-sixth of the American economy”.

“I think we’ll have ample opportunity to read and amend the bill,” Mr McConnell had said the previous day.

“Will it be more than 10 hours?” Mr Schumer responded.

“I think we’ll have ample opportunity to read and amend the bill,” Mr McConnell repeated.

Since Republicans are using a process known as reconciliation to try to pass their healthcare measure, meaning they only need 51 votes in support of the legislation instead of the normal 60, a maximum of 20 hours of debate is allowed – 10 for each political party.

Each hour represents 2.3 million Americans losing their insurance each year over the next 10 years, Mr Schumer said, referring to the Congressional Budget Office’s estimate that the House of Representatives’ healthcare bill, which narrowly passed in the lower chamber of Congress in May, would kick 23 million people off their insurance plans by 2026.

Meanwhile, Republicans have called Obamacare – officially known as the Affordable Care Act – “unsustainable”, citing skyrocketing premiums and the unstable health insurance marketplaces created by the law.

Mr Schumer pointed out on Tuesday that the majority leader has not yet clarified whether the Democrats' 10 hours for debate would be on the House’s healthcare bill or on the Senate’s version.

While Republican senators aren’t voicing objections to the process as fiercely as Democrats, some, including Senator Marco Rubio, have said that the bill should eventually be subject to an open debate.

Thousands march against Donald Trump in LGBT rights parade Show all 8 1 /8 Thousands march against Donald Trump in LGBT rights parade Thousands march against Donald Trump in LGBT rights parade A marcher hold a sign that reads "Love is Love is Love" on the National Mall with the Washington Monument in the background during the Equality March for Unity and Pride in Washington AP Thousands march against Donald Trump in LGBT rights parade Marchers unfurl a huge rainbow flag as they prepare to march in the Equality March for Unity and Pride in Washington AP Thousands march against Donald Trump in LGBT rights parade Marchers gather to hear speakers at the end of the Los Angeles LGBTQ #ResistMarch AP Thousands march against Donald Trump in LGBT rights parade Gil Mendez, of San Francisco, holds a sign to honor the victims of the shooting at the Pulse Nightclub in Orlando as he marches during the Equality March for Unity and Pride in Washington AP Thousands march against Donald Trump in LGBT rights parade An demonstrator looks on as LGBT members and their supporters take part of the Equality March for Unity AFP/Getty Images Thousands march against Donald Trump in LGBT rights parade A marcher listens to speakers at the end of the Los Angeles LGBTQ #ResistMarch AP Thousands march against Donald Trump in LGBT rights parade LGBT members and their supporters take part of the Equality March for Unity AFP/Getty Images Thousands march against Donald Trump in LGBT rights parade A marcher mugs for the camera during the Los Angeles LGBTQ #ResistMarch AP

“If it's an effort to rush it from a small group of people straight to the floor on an up or down vote, it'll be a problem,” Mr Rubio told CNN.

Mr McConnell has made clear that he wants to have a vote on the legislation before senators leave Washington DC for the Fourth of July. A draft of the measure is expected to be completed this week.

With a majority of 52 senators, Mr McConnell can only afford to lose two Republican votes on the bill. This may be difficult in the upper chamber, where different members of the party are divided on whether Medicaid – a healthcare programme for the poor – should be protected or trimmed down. In the event of a 50-50 tie, Vice President Mike Pence would be the deciding vote.

“What we know right now is that the final timeline will simply be when we get 50 votes plus having the vice president in town,” Republican senator Mike Rounds told reporters. “So that’ll be the final decision, I think. I know there’s a real desire on the part of leadership to have the vote before the Fourth of July. I think it’s a good goal to have, but we’re going to wait and see what it looks like.”

Along with expressing concerns about the possibility of limited debate, Democrats have also blasted Republicans for drafting their healthcare measure behind closed doors, arguing that the passage of President Barack Obama’s signature healthcare law was preceded by more than a year of public hearings in the Senate.

“In 2010, even though no Republicans voted for it, at least they had input,” Democratic senator Joe Manchin said. “My take is let us be involved so we can work together.”

“Let’s have hearings. Let’s have openness,” he added, saying that he hopes the Republicans’ bill is unsuccessful. “If it fails, I think some good moderate Republicans will sit down with some good moderate Democrats and try to find a pathway forward to fix it.”

During a White House press briefing, Press Secretary Sean Spicer said Mr Schumer made it clear that Democrats did not want to part of a process to repeal and replace Obamacare.