AUGUSTA — Democratic legislators are signing onto a “friend-of-the-court” brief to express support for the federal Affordable Care Act as it heads to a showdown in the U.S. Supreme Court.

Gov. Paul LePage and other governors have challenged the constitutionality of the law, which opponents have branded “Obamacare.” Much of the dispute focuses on a mandate that Americans buy health insurance if they can afford it.

The Supreme Court is expected to hear arguments in the case this summer.

While many governors have registered their support for the legal challenge, more than 400 lawmakers from around the country have signed an amicus brief supporting the law’s constitutionality.