WASHINGTON (AP) — Supreme Court justices peppered opponents of President Barack Obama's health care law with skeptical questions during oral arguments Wednesday on the latest challenge to the sweeping legislation.

Justice Anthony Kennedy, whose vote is seen as pivotal, suggested that the plaintiffs' argument raises a "serious" constitutional problem affecting the relationship between states and the federal government.

The plaintiffs argue that only residents of states that set up their own insurance markets can get federal subsidies to help pay their premiums.

The courts' liberal justices also expressed doubt during Wednesday's oral arguments.