The Supreme Court on Monday allowed Virginia to prevent mining of the largest deposit of uranium in the United States, in an opinion that highlighted sharp divisions among the justices about how they should evaluate the motivations of lawmakers.

The case turned on the regulatory line between state and federal authority over the extraction and then further processing of nuclear materials. Six of the justices agreed that a 1954 federal law, known as the Atomic Energy Act, did not preempt a state ban on mining.

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But those justices split evenly among two competing opinions over discussions of the court’s role in inquiring about the intentions of state and federal lawmakers — the latest skirmish in the fight about judicial philosophy and the role of the Supreme Court when reviewing laws.

Justice Neil M. Gorsuch, in an opinion joined by Justices Clarence Thomas and Brett M. Kavanaugh, spends pages warning against the court looking into lawmaker motivations, noting that Congress left untouched the authority of states to regulate mining on private land in their borders.

“And we are hardly free to extend a federal statute to a sphere Congress was well aware of but chose to leave alone,” Gorsuch wrote. “In this, as in any field of statutory interpretation, it is our duty to respect not only what Congress wrote but, as importantly, what it didn’t write.”

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Justice Ruth Bader Ginsburg, in an opinion joined by Justices Sonia Sotomayor and Elena Kagan, wrote that she agreed with much of Gorsuch’s opinion “but his discussion of the perils of inquiring into legislative motive” sweeps beyond the confines of this case “and therefore seems to me inappropriate in an opinion speaking for the Court.”

Gorsuch fired back in a footnote to his opinion, saying considerations about intent “are, to us, essential to its resolution.”

Gorsuch wrote that Congress might have had disparate or conflicting goals in mind when it voted to enact the 1954 law, and might have different views on how Virginia’s law conflicted with their purposes. But, he wrote, “The only thing a court can be sure of is what can be found in the law itself.”

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In a dissent, Chief Justice John G. Roberts Jr., joined by Justices Stephen G. Breyer and Samuel A. Alito Jr., concludes that the federal law prohibited states from banning mining as an indirect way to regulate other aspects of the uranium process, including milling and tailings.

Monday’s decision cuts against the Trump administration, which argued in November that allowing the Virginia ban without reviewing the state’s purpose would amount to “giving states a roadmap for undermining a multi-billion-dollar industry.”

And three Republican senators had contended in a brief to the Supreme Court that allowing the state ban could undermine federal policy about uranium and other assets that are critical to national security and defense.

Senate Armed Services Chairman James M. Inhofe of Oklahoma, along with Tom Cotton of Arkansas and Ted Cruz of Texas, had urged the justices to side with the mining company because a decision that allows a state ban to continue would carry “far-reaching and serious risks” at a time when domestic production and development of uranium is at historic lows.