The U.S. Supreme Court on Monday blocked Commerce Secretary Wilbur Ross from having to sit for a deposition in a lawsuit challenging the Trump administration’s decision to add a question about citizenship to the 2020 census.

The brief order from the court is a victory for the Trump administration, which fought hard to block Ross from having to answer questions under oath. It’s a major blow to the plaintiffs in the suit, a coalition of states, cities and immigrant groups that say the way the question was added violates the U.S. Constitution and federal law.

In testimony before Congress and in a memo announcing the question, Ross said the administration added the question at the request of the Department of Justice so that the department could better enforce the Voting Rights Act. But documents disclosed in the lawsuit show Ross was interested in adding the question months before the Justice Department made its request, and that he discussed it with Steve Bannon, a top White House adviser.

Ross’ deposition could have provided key insights into those conversations and how the decision was made. The plaintiffs likely would have used it to make their case that the Justice Department request was a pretext and that Ross, who has control over the Census Bureau, was set on adding the citizenship question before he even instructed census officials to study the possibility of doing so.

Civil rights groups strongly oppose the decision to add the citizenship question, saying immigrants will be less likely to respond to the census because they are fearful about giving information about their own immigration status or the status of a loved one to the Trump administration.

They say the question has a “discriminatory purpose” in violation of the Constitution’s due process protections, and that Ross violated federal law by deciding to add the question before the Census Bureau had reviewed it.

An inaccurate census would have severe consequences. The survey helps determine how hundreds of billions of dollars in federal funds are allocated, and how political districts are drawn. While the Census Bureau does ask about citizenship through the American Community Survey, which only goes out to a small percentage of households each year, it has not asked about citizenship on the decennial census, which goes out to every American household, since 1950.

It is not common for federal judges to order high-ranking government officials, including Cabinet secretaries, to sit for depositions. But U.S. District Judge Jesse Furman, the trial judge who is overseeing the case in New York, ordered Ross in September to sit for one. He reasoned that Ross’ “intent and credibility are directly at issue in these cases.”

“The concededly relevant inquiry into ‘Commerce’s intent’ could not possibly be conducted without the testimony of Secretary Ross himself,” Furman wrote in September. “Critically, that is not the case merely because Secretary Ross made the decision that Plaintiffs are challenging. ... Instead, it is the case because Secretary Ross was personally and directly involved in the decision, and the unusual process leading to it, to an unusual degree.”

The U.S. Court of Appeals for the 2nd Circuit upheld Furman’s decision in October.

Attorney General Jeff Sessions strongly criticized Furman’s ruling in a speech to the Heritage Foundation this month, saying it was an example of the federal courts overstepping their authority.

“The probing discovery of the kind ordered in the Census case is just the kind of intrusion Hamilton warned against,” Sessions said, according to prepared remarks. “And we are seeing it in case after case. When a hot-button policy issue ends up in litigation, judges are starting to believe their role is to examine the entire process that led to the policy decision — to redo the entire political debate in their courtrooms.”

The trial in the New York case is scheduled to begin in early November. There are also separate federal lawsuits in California and Maryland seeking to block the question from being added.