The Supreme Court’s conservative majority seemed skeptical Wednesday as the Environmental Protection Agency sought to continue enforcing an anti-air-pollution rule in 11 states while separate legal challenges proceed around the country.

The EPA’s “good neighbor” rule is intended to restrict smokestack emissions from power plants and other industrial sources that burden downwind areas with smog-causing pollution.

Three energy-producing states — Ohio, Indiana and West Virginia — challenged the rule, along with the steel industry and other groups, calling it costly and ineffective. The rule is on hold in a dozen states because of the court challenges.

The Supreme Court, with a 6-3 conservative majority, has increasingly reined in the powers of federal agencies, including the EPA, in recent years. The justices have restricted EPA’s authority to fight air and water pollution — including a landmark 2022 ruling that limited EPA’s authority to regulate carbon dioxide emissions from power plants that contribute to global warming. The court also shot down a vaccine mandate and blocked President Joe Biden’s student loan forgiveness program.

The court is currently weighing whether to overturn its 40-year-old Chevron decision, which has been the basis for upholding a wide range of regulations on public health, workplace safety and consumer protections.

A lawyer for the EPA said the “good neighbor” rule was important to protect downwind states that receive unwanted air pollution from other states. Besides the potential health impacts, the states face their own federal deadlines to ensure clean air, said Deputy U.S. Solicitor General Malcolm Stewart, representing the EPA.

States such as Wisconsin, New York and Connecticut can struggle to meet federal standards and reduce harmful levels of ozone because of pollution from power plants, cement kilns and natural gas pipelines that drift across their borders.

Judith Vale, New York’s deputy solicitor general, said as much as 65% of some states’ smog pollution comes from out of state. The EPA plan was intended to provide a national solution to the problem of ozone pollution, but challengers said it relied on the assumption that all 23 states targeted by the rule would participate.