(Washington) (AP) — The Supreme Court seemed reluctant Monday to agree with companies seeking to overturn a decades-old Virginia ban on mining radioactive uranium.

The justices heard arguments in a case brought by the owners of a massive uranium deposit in Pittsylvania County, Virginia. It’s the largest known uranium deposit in the United States, and its owners have said it contains enough uranium to power all of the country’s nuclear reactors continuously for two years.

Virginia says nothing in the federal Atomic Energy Act keeps it from banning uranium mining, which it has done since the 1980s. But the uranium companies argue that the state’s purpose in passing the ban was improper. The companies argue the state can’t ban uranium mining based on concerns about radiological hazards connected with what happens next: processing the radioactive uranium and storing the radioactive waste that results. Virginia says its purpose doesn’t matter.

During arguments Monday, both liberal and conservative justices seemed to voice concerns about wading into lawmakers’ motives in passing the mining ban. Conservative Justice Neil Gorsuch and Chief Justice John Roberts and liberal justices Elena Kagan and Sonia Sotomayor all seemed to raise issues with doing so.

Though Virginia’s uranium mining ban has been in place for decades, the deposit’s owners first sued over it in 2015. That’s in part because a few years after the deposit was discovered, the price of uranium plummeted and interest in mining it had waned. But after the price of uranium rebounded, the deposit’s owners attempted to convince Virginia lawmakers to reconsider the ban from 2008 to 2013. After that effort failed, they sued the state in federal court in an attempt to invalidate the ban and clear the path for mining the uranium, which they say is worth several billion dollars.