House Republicans to introduce health care legislation this week

— -- House Republicans are expected to introduce legislation to repeal and replace the Affordable Care Act early this week, a senior GOP aide tells ABC News.

Congressional staffers worked through last week tweaking the proposal. House Speaker Paul Ryan discussed the plan with Health and Human Services Secretary Tom Price, Office of Management and Budget Director Mick Mulvaney and Energy and Commerce Committee Chairman Greg Walden on Saturday, according to the aide.

Some Republican lawmakers expressed concern last week about the House's draft legislation -- with opposition forming against a proposed refundable tax credit to help people buy insurance. One group of GOP senators is apprehensive about phasing out Obamacare's Medicaid expansion.

But Ryan last Friday said he wasn't "worried at all" about the status of the GOP's health care reform plan.

"We got a choice to make. Do we want to keep Obamacare, or do we want to repeal and replace Obamacare?" Ryan said on Fox News, adding that the GOP and President Trump were "working off the same piece of paper" with respect to health care reform.

In January, then-President elect Trump promised his party would repeal Obamacare -- his predecessor's signature legislative achievement -- and replace it "almost immediately" with a plan that would cover "everybody."

Under budgetary rules, Republicans will need just 51 votes to repeal Obamacare in the Senate. Given Vice President Mike Pence's tie breaking vote, they can only afford to lose two GOP senators.