The US Supreme Court opened its new term on Monday by weighing whether federal law blocks Colorado communities from pursuing state-law damages claims against ExxonMobil and Suncor Energy over alleged climate harms.

The dispute, Suncor Energy v County Commissioners of Boulder County, could determine the viability of dozens of similar lawsuits brought by states and local governments seeking compensation from fossil-fuel producers for costs associated with a warming climate. Eight justices heard two hours of argument after Justice Samuel Alito recused himself.

Questions from the bench showed the court wrestling with both the reach of federal authority over interstate emissions and whether Boulder’s claims can survive if they are framed around the sale and marketing of fossil fuels rather than direct regulation of greenhouse gases.

Chief Justice John Roberts pressed Boulder’s lawyer, Kevin Russell, about the potential nationwide consequences of allowing the action to proceed, suggesting municipalities across the country could file comparable suits. Other justices explored whether claims involving alleged failures to warn consumers might remain within traditional state powers even if broader emissions-based claims are barred.

Boulder County, the city of Boulder and San Miguel County filed the lawsuit in Colorado state court in 2018. They accuse Exxon and Suncor of contributing to climate-related damage while misleading consumers about risks associated with fossil-fuel products. The local governments seek relief to cover costs they attribute to effects including extreme heat, drought, wildfire and flooding.

The companies deny that Colorado law can be used to impose liability for harms allegedly arising from worldwide greenhouse-gas emissions. Their lawyer, Kannon Shanmugam, argued that interstate and international emissions are inherently federal matters and that state-law claims cannot be used to govern conduct beyond Colorado.

The Trump administration backed the companies. Principal Deputy Solicitor General Sarah Harris, arguing for the federal government, supported the position that federal law precludes state claims that effectively seek redress for the effects of interstate emissions.

Boulder countered that its case does not seek to regulate emissions or dictate national energy policy. Russell told the court that the communities are pursuing traditional state-law remedies against companies for alleged injuries connected to products sold in Colorado and alleged failures to disclose their dangers.

The distinction occupied the argument. Some justices questioned whether courts could separate product-related allegations from the global emissions that ultimately produce the claimed climate damage. Others appeared wary of extinguishing state tort claims merely because the alleged injury has a nationwide or international dimension.

The case reaches the justices after the Colorado Supreme Court allowed Boulder’s claims to proceed. The US Supreme Court agreed in February to hear the companies’ appeal and directed the parties also to address whether the justices have statutory and constitutional jurisdiction to decide the dispute.

That jurisdictional question created another route for a narrow outcome. Several justices examined whether the Colorado ruling was sufficiently final for Supreme Court review before the state litigation has run its course. A decision declining jurisdiction could leave the Colorado proceedings alive without resolving the broader pre-emption question.

Alito’s absence adds uncertainty. The court normally has a 6-3 conservative majority, but only eight justices are participating. A 4-4 division would affirm the Colorado Supreme Court’s judgment without creating a binding nationwide Supreme Court precedent.

The litigation is being closely watched because nearly 60 climate-related cases involving fossil-fuel companies are pending around the country, though their legal theories and procedural positions differ. State and municipal plaintiffs have generally sought damages or other remedies under state statutes and common law, while defendants have repeatedly argued that claims tied to global emissions belong under federal law.

The companies rely partly on Supreme Court precedents holding that federal common-law claims over interstate greenhouse-gas emissions were displaced by the Clean Air Act, which assigns regulatory authority to the Environmental Protection Agency. Boulder argues those decisions do not erase independent state-law causes of action concerning products and alleged deception.