(Bloomberg) -- The U.S. Supreme Court rejected a bid by Maine toescape one requirement of Obamacare, as the justices prepare torule on a more far-reaching challenge that might unravel the healthcare law.

The justices Monday left intact a federal appeals court decisionthat said Maine must continue offering Medicaid coverage to youngadults until 2019.

The dispute turned on an Obamacare provision that requiresstates to maintain their existing eligibility standards forchildren as a condition of receiving federal dollars under theMedicaid health-care program for the poor.

Maine’s top health official, Mary Mayhew, sought to drop thestate’s longstanding Medicaid coverage for 19- and 20-year- olds.The Obama administration refused to allow the change, pointing tothe Affordable Care Act provision.

Mayhew sued, arguing that the state was being unconstitutionallycoerced into keeping that coverage. A Boston- based federal appealscourt rejected that argument.

The Supreme Court will rule by the end of the month in itscurrent Obamacare case, a dispute over the reach of the taxsubsidies the law created to make insurance affordable. A group ofchallengers contends the law allows subsidies in only about a thirdof the states, those that have set up their own online exchangesfor people to buy policies.

A variation of the coercion argument was before the SupremeCourt three years ago, when it considered a broad constitutionalchallenge. One aspect of that ruling said the federal governmentcan’t threaten to withhold existing Medicaid funds from states thatrefuse to expand the program to cover people at higher incomelevels.

The appeals court in the Maine case said that state’s situationwas different because it wasn’t being required to expandcoverage.

The case is Mayhew v. Burwell, 14-992.

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