Maine has stepped into a highly politicized case that could affect millions of people, joining 21 other states and the District of Columbia in a brief filed before the U.S. Supreme Court arguing in favor of maintaining health insurance subsidies for the residents of all states under the Affordable Care Act.

The Supreme Court is scheduled next month to hear an argument to eliminate subsidies for the 36 states – including Maine – that chose to not establish state-run health care marketplaces, leaving their citizens to purchase the required insurance on the federally run exchange, healthcare.gov.

The case before the court stems from the subsidies that people receive in the form of a tax credit from the IRS. A provision in the ACA limits the subsidies to “an exchange established by the state.” The plaintiffs argue that the purpose of the tax-credit provision was to induce states to create their own health care marketplaces, and that the IRS is illegally giving the subsidies to people in the 36 states because they signed up for coverage on an exchange created by the federal government.

Supporters of the ACA say Congress intended for state and federally run exchanges to be treated equally, and that the plaintiffs are trying to dismantle the law through a technicality.

If the Supreme Court rules in the plaintiffs’ favor, more than 6 million people would lose their subsidies, and many also would probably lose their insurance, putting the viability of the ACA in question.

Why Maine joined in the fight to save an integral component of the ACA is unclear.

Gov. Paul LePage has blocked attempts by Democratic and some moderate Republican lawmakers to expand Medicaid – another facet of the ACA. State officials, including those representing LePage, couldn’t be reached for comment Monday.

Without subsidies, many who have gained insurance through the ACA would no longer be able to afford premiums that can reach $400 or more per month without government assistance. With subsidies, many people purchasing individual insurance pay between $100 and $200 per month.

The “friend of the court” brief, signed by Maine Attorney General Janet Mills, was filed Jan. 28 in the “King vs. Burwell” case that’s scheduled to go before the Supreme Court on March 4 and is likely to be decided this summer. Mills couldn’t be reached for comment Monday.

“Friend of the court” filings are submitted by those who are not parties to the court case but have an interest in the outcome and want the Supreme Court to consider their opinion.

Nearly 90 percent of the more than 61,000 people in Maine who have so far signed up for 2015 insurance through the ACA qualify for subsidies, which extend to those earning up to 400 percent of the federal poverty level, or about $90,000 for a family of four.

“It would really erode the effectiveness of the program if the subsidies didn’t exist,” said Kevin Lewis, CEO of Maine Community Health Options, one of the insurers on the Maine marketplace. “It would make it that much tougher for people to afford insurance.”

A national group representing co-operatives like Maine Community Health Options also has filed a “friend of the court” brief advocating for the subsidies to remain.

Meanwhile, Maine is joining the federal government and the 21 other states in arguing that the intent of lawmakers crafting the law was to provide subsidies to everyone signing up for insurance – not to create separate insurance benefits for those who enroll through state-based versus federally run marketplaces.

Whether Mills and LePage agree on the “King vs. Burwell” case is unclear. LePage spokeswoman Adrienne Bennett said Monday that she could not provide any clarity on the issue because she hasn’t spoken with the governor about the topic.

Many conservative politicians have relentlessly criticized the ACA and have lobbied to repeal the law.

Lewis is pleased that Maine is joining states working to preserve the ACA.

“I think it’s vitally important that we all weigh in so people can have better access to coverage,” he said. Without subsidies, fewer healthy people would enroll, making coverage more expensive because the remaining insurance pool would contain sicker people, Lewis said.

Trish Riley, executive director of Maine and Washington-based National Academy for State Health Policy, a health policy think tank, said it’s important for many groups to give their opinion on the case, letting the Supreme Court know the practical impact of cutting off subsidies for millions of people.

“The reality is, if this happens there would be millions who have insurance who could no longer afford their premiums. What would happen to those people?” Riley said.