Senators Mike Lee and Jerry Moran each announced they could not support the bill in its current form, bringing to four the number of Republican senators opposed and effectively killing the revised version of the bill.
Two more US Republican lawmakers announced their opposition on Monday to the Senate's Obamacare repeal bill, all but killing the plan in its current form and potentially dealing a monumental setback to President Donald Trump.
"My colleague @JerryMoran and I will not support the MTP (motion to proceed) to this version of BCRA #HealthcareBill," conservative Senator Mike Lee said on Twitter.
Republicans control 52 of the Senate's 100 seats. Democrats are united against the controversial legislation, while Republicans Susan Collins and Rand Paul declared their opposition last week.
Republican leadership could afford no more defectors.
But with Lee and Moran adding their names to that list, the bill has no chance of even getting a vote on the Senate floor unless the Senate Majority Leader Mitch McConnell decides to make significant changes to woo skeptics back into the fold.
McConnell at the weekend delayed a vote to proceed on the bill, after Republican Senator John McCain underwent surgery for a blood clot and said he would recuperate at home in Arizona for at least a week.