AUGUSTA — Public opinion played no role in Maine’s decision to join the 25 other states that are challenging the federal health care law, state Attorney General William Schneider says.

“Honestly, for me, it’s a matter of principle. It’s a matter of fact that I believe, as do the other 25 attorneys general, that this portion of the law is unconstitutional,” Schneider said in an interview Monday.

“And it’s my duty to do whatever I can to make sure that that does not take effect. It really doesn’t matter whether it’s popular or not. It’s my duty to address a federal law that’s going to have an effect on the people of Maine if I think it’s unconstitutional,” he said.

Schneider said he finds the mandate for Americans to buy health insurance starting in 2014 or pay penalties “the most egregiously unconstitutional part of the law.”

Schneider was interviewed as the U.S. Supreme Court opened three days of arguments on the Affordable Care Act. On Wednesday, he and other attorneys general from states that are challenging the law will be in court to observe arguments before the justices.

Although he will have no active role, Schneider said he sees an important symbolic role representing Mainers.

He and the other plaintiff states have combined efforts “to create and craft the arguments” being made before the court, he said. The mandate for health insurance differs from states’ requirements that motor vehicle owners get insurance, Schneider said.

The U.S. Constitution recognizes that all the power in the United States rests with the people and that the people give the federal government “a certain limited set of powers,” he said.

“Any power that’s not given to the federal government is reserved to the people of the states, so the states have a different set of powers than the federal government does. And the states can do that kind of thing,” such as mandating car insurance, Schneider said.

The Affordable Care Act now has legal standing in its entirety, but the Supreme Court could find that the mandate is unconstitutional and connected to the rest of the law, which would, in effect, throw out the entire law, Schneider said.

“If it’s found severable, then Congress may want to revisit the Affordable Care Act and figure out what that means,” Schneider said. “If it’s found not severable, Congress will probably have to go back to the drawing board and address health care in a big way again.”