BOSTON — Massachusetts could lose billions of dollars under the latest effort to repeal and replace Obamacare, which specifically singles out blue states that have expanded Medicaid coverage under the federal law.

As early as next week, the Senate could take up a proposal by Sens. Bill Cassidy of Louisiana and Lindsey Graham of South Carolina to repeal major pillars of former President Barack Obama’s signature health care law, replacing them with block grants that leave it to states to design their own programs.

As of Friday, it wasn’t clear if Republicans had enough votes to pass the proposal.

Gov. Charlie Baker, a Republican, has joined other governors in resisting it. He testified in opposition to the bill before a congressional committee this month.

“We’re talking billions and billions of dollars over the course of the next five years,” he told lawmakers, describing the state’s potential loss.

“The problem I have with the Graham-Cassidy piece is that it assumes the cost of health care across the country should be the same everywhere,” he said.

Dr. John McDonough, a professor of public health practice at the Department of Health Policy and Management at Harvard, said Massachusetts and 30 other states that expanded Medicaid programs under the Affordable Care Act would be hit especially hard by the latest plan.

“The deliberate intent of this law is to redistribute money from the states that expanded Medicaid to those that didn’t,” he said.

For Massachusetts, that could mean losing $5 billion in federal funding by 2026 under the latest repeal plan, and $8.7 billion the following year.

While ending Obamacare’s Medicaid expansion, the Graham-Cassidy bill also would eliminate the individual and employer health care mandates and slash subsidies to lower health care costs.

It also waives Obamacare provisions that require coverage of benefits such as emergency services, maternity care and substance abuse treatment.

Health care advocates said the Graham-Cassidy bill will narrow choices for women seeking reproductive and other medical services.

“The Graham-Cassidy bill is the worst Trumpcare bill yet,” said Dr. Jennifer Childs-Roshak, president and CEO of the Planned Parenthood League of Massachusetts. ”This dangerous scheme would limit access to birth control, cancer screenings, STD testing and treatment, making it harder for the most vulnerable members of our communities to stay healthy and take care of themselves.”

Nationwide, the Center on Budget and Policy Priorities expects more than 32 million Americans would lose insurance as a result of the proposed changes, which President Trump has pledged to sign into law.

In a joint statement, the nonprofit group Health Care for All, Associated Industries of Massachusetts and the Massachusetts Medical Society warned that the latest repeal plan will severely strain the state’s budget and leave tens of thousands of residents — including seniors, children and people with disabilities — without access to quality, affordable health care.

“Moreover, by overturning protections for patients with preexisting conditions and by slashing essential health benefits, the bill would make it so that even patients that still have coverage might be unable to access meaningful care,” the statement read.

The Affordable Care Act was loosely based on Massachusetts’ health care system, which was signed into law in 2006 by Gov. Mitt Romney. The Obamacare law has extended coverage to 20 million Americans, prohibited insurers from denying coverage to people with pre-existing conditions, and allowed young adults to stay on their parents’ plans until age 26.

In Massachusetts, more than 190,000 people are enrolled in subsidized insurance through the state’s Health Connector. The state’s Medicaid program, MassHealth, covers more than 1.9 million people, including 300,000 added as a result of the federal law.

Massachusetts has the highest rate of insured people in the nation, with 97.5 percent of residents having either private, employer or government-backed medical coverage last year, according to the U.S. Census Bureau.

Congressional Republicans have pushed for years to repeal Obamacare, but they’ve been unable to muster the votes necessary to get across the finish line, even with a majority in both houses of Congress and a Republican in the White House.

Moderates worry about people losing access to health care; conservatives say the plans don’t go far enough.

Senate Republicans defeated an effort earlier this year to repeal Obama’s law, which had been approved by the House.

Congress is rushing to take action on the latest bill by Sept. 30, when special rules that prevent Democrats from filibustering will expire.

As of Friday, the new bill didn’t have the public support of 50 senators necessary to advance, but Trump told reporters he is growing more confident that it will pass.

“Obamacare is a disaster. It’s failing badly,” he said this week. “You look at what’s happening with premiums for people, they can’t afford Obamacare.”

Still, supporters of the measure were dealt a blow Friday when Sen. John McCain, R-Ariz., said he won’t vote for it.

“I believe we could do better working together, Republicans and Democrats, and have not yet really tried,” McCain said in a statement. “Nor could I support it without knowing how much it will cost, how it will effect insurance premiums, and how many people will be helped or hurt by it.”

Christian M. Wade covers the Massachusetts Statehouse for North of Boston Media Group’s newspapers and websites. Email him at cwade@cnhi.com.