The landmark Juliana v. United States trial, which pits 21 children and young adults against the Trump administration, was supposed to begin this week in US District Court in Oregon. Now it’s unclear whether the Supreme Court will allow the case to proceed to trial—and if so, when that will happen.

The youths and their attorneys filed the case in 2015 (originally against the Obama administration), arguing that the federal government’s actions are contributing to climate change, violating the youngest generation’s constitutional rights, and failing to protect essential public trust resources; they have asked the courts to compel the government to move swiftly to stabilize the climate system. In response, the government’s latest filing admits that climate change is causing a variety of negative impacts, but its lead attorney has argued that climate policy is the job of the legislative and executive branches of government—not the judiciary.

The federal government has made numerous attempts to have the kids’ climate case dismissed or delayed by the Ninth Circuit Court of Appeals, and this is the second time in three months that government attorneys have petitioned the Supreme Court to intervene. Now-retired Associate Justice Anthony Kennedy denied the earlier request. This time around, Chief Justice John Roberts issued a temporary stay on October 19 that will stay in place until “further order of The Chief Justice or of the Court.”

Hoping that Roberts would lift the stay in time for the trial to begin on schedule, the plaintiffs filed their response at the beginning of last week, and the administration filed its reply two days later. The ball is now entirely in the Supreme Court. According to a report by Vox, “what happens next is unclear, including whether the other justices on the bench will weigh in.” Legal experts told Vox that “it is extremely unusual for the Supreme Court to step in to block a legal proceeding in a lower court.” Meanwhile, the trial has been “vacated,” meaning that there is no longer an official start date.

“Why the government appears so frantic to avoid the trial has been an overriding, and unanswered, question,” writes investigative journalist Karen Savage in Climate Liability News. “But part of the reason could be that the case puts the government in an uncomfortable legal position. Much of the evidence used by the young people to prove they are being harmed by climate change comes from the government itself.”