WASHINGTON, D.C.: The U.S. Supreme Court considered on October 5 whether ExxonMobil and Suncor Energy can block a Colorado climate lawsuit, in a case that could affect dozens of similar actions seeking billions of dollars from fossil fuel companies.

The case was heard as the court's 6-3 conservative majority began its new nine-month term. Exxon and Suncor appealed after the Colorado Supreme Court allowed a lawsuit brought by the city and county governments of Boulder to proceed.

"This case involves an unprecedented effort to use state law to regulate global conduct," Kannon Shanmugam, a lawyer for the oil companies, told the justices.

Boulder is suing the companies under Colorado law, Shanmugam added, "on the theory that their global conduct increased the global use of fossil fuels, which led to an increase in global greenhouse gas emissions, which contributed to global climate change, which resulted in global harms."

"Our constitutional system does not permit state law to be used in that manner. The Constitution bars the application of state law to certain inherently federal areas," Shanmugam said.

Boulder's city and county governments have accused Exxon and Suncor of helping drive climate change and misleading the public about the risks of fossil fuels. They are seeking to hold the companies liable for past and future costs associated with climate change, including infrastructure repairs, environmental damage, emergency management and harm to public health.

President Donald Trump's administration has backed Exxon and Suncor, arguing that the federal government's authority to regulate air pollution precludes Boulder's claims.

"Interstate air pollution is an inherently federal area," said Sarah Harris, a Justice Department lawyer representing the Trump administration, adding that Congress has not authorized the Boulder lawsuit under a key provision of the Clean Air Act.

"Second, this suit egregiously exceeds constitutional limits on state authority," Harris told the justices.

Conservative Chief Justice John Roberts questioned the argument that state lawsuits are barred when similar litigation has previously been allowed.

"I guess I'm not quite sure what makes this situation different from all those other ones where we've allowed (it)," Roberts told Harris.

Nearly 60 state and local governments have filed similar lawsuits seeking billions of dollars from fossil fuel companies, Exxon and Suncor told the justices. A Supreme Court ruling siding with the companies could lead to many of those cases being dismissed.

Liberal Justice Ketanji Brown Jackson questioned whether the case had reached the Supreme Court too soon.

"I understand that you have several other federal issues that you have raised that are still pending in the state court. So why shouldn't we wait and hear all of these claims once the state courts are done with their federal considerations?" Jackson asked Shanmugam.

"I would submit," Shanmugam replied, "that given the extraordinary magnitude of these cases, where in each of these cases plaintiffs are seeking billions of dollars of damages, that we need an answer to this question sooner rather than later."

Energy companies and trade groups, along with allied states, have built a largely winning record before the justices over the past two decades in cases involving climate liability and the reach of federal environmental regulation.

Conservative Justice Samuel Alito has recused himself from the case, meaning eight justices will decide it. Alito owns stock in several oil and gas companies but not Exxon or Suncor, according to his financial disclosure forms.

The Supreme Court is expected to decide by the end of June.