WASHINGTON (Reuters) - The Trump administration’s move on Wednesday to rescind guidance allowing transgender students to use the bathrooms of their choice has raised the stakes for an upcoming U.S. Supreme Court case that could deliver a landmark decision on the issue.

Women chant during a protest against the Trump administration's move to rescind guidance allowing transgender students to use the bathrooms of their choice, in Manhattan, New York, U.S., February 23, 2017. REUTERS/Bria Webb

The eight justices are due to hear oral arguments on March 28 on whether the Gloucester County School Board in Virginia can block Gavin Grimm, a female-born transgender high school student, from using the boys’ bathroom. A ruling is due by the end of June.

A key question in the case is whether a federal law, known as Title IX, which bars sex discrimination in education, covers transgender students. The Education Department under Democratic President Barack Obama said in guidance to public schools last May that it does, but the Republican Trump administration withdrew that finding on Wednesday.

The high court on Thursday asked the lawyers involved to file letters by March 1 giving their views on how the Trump action should affect consideration of the case.

Lawyers for Grimm say that the definition of sex discrimination in Title IX is broad and includes gender identity. The school board maintains that the law was enacted purely to address “physiological distinctions between men and women.”

If the Supreme Court rules that Title IX protects transgender students, the decision would become the law of the land, binding the Trump administration and the states.

“This is an incredibly urgent issue for Gavin and these other kids across the country,” said Joshua Block, a lawyer with the American Civil Liberties Union (ACLU) who represents Grimm.

The Trump administration’s announcement “only underscores the need for the Supreme Court to bring some clarity here,” he added.

The administration on Wednesday did not offer its own interpretation of Title IX, with the Justice Department telling the court only that it plans to “consider further and more completely the legal issues involved.”

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The administration is not directly involved in the case.

Lawyers for both Grimm and the Gloucester County School Board have urged the court to decide whether Title IX applies to transgender students rather than taking a narrower approach by sending the case back to a lower court.

In a court filing on Thursday, the ACLU said that, regardless of the administration’s position, the court “can - and should - resolve the underlying question of whether the Board’s policy violates Title IX.”

The school board’s lawyers made similar comments in their most recent court filing, saying that the meaning of the federal law is “plain and may be resolved as a matter of straightforward interpretation.”

But the court could take a more cautious approach and send the case back to the Richmond, Virginia-based 4th U.S. Circuit Court of Appeals. That court’s April 2016 ruling in favor of Grimm relied on the Obama administration’s interpretation of the law.

Kyle Duncan, a lawyer representing the school board, said the court must at a minimum throw out the appeals court decision because “the entire basis for that opinion” was the no-longer extant Obama administration interpretation.

JUSTICE KENNEDY: PIVOTAL VOTE?

With the eight-justice court likely to be closely divided, Trump’s Supreme Court nominee, conservative appeals court judge Neil Gorsuch, could end up casting the deciding vote if he is confirmed by the U.S. Senate in time. Otherwise, the court, which is divided equally between liberals and conservatives, could split 4-4, which would set no nationwide legal precedent.

Clues as to how the high court could rule can be gleaned from its decision last August to temporarily block the appeals court decision in Grimm’s case from going into effect. That emergency request from the school board did not require the justices to decide the merits of the case.

The vote in favor of the school board was 5-3, with Justice Stephen Breyer, a liberal, joining the four conservative justices. Breyer made clear in a statement at the time that his vote would not dictate how he would approach the case if the court took the issue up.

That decision indicated that the court is likely to be closely divided at oral argument. Grimm’s hopes may rest in Justice Anthony Kennedy, a conservative who voted against Grimm last summer but has sometimes sided with liberals in major cases, including several on gay rights.

But even lawyers closely following the case are not sure which way Kennedy could go.

“If I could predict that, I would be down in the casino,” said Gary McCaleb, a lawyer with conservative Christian legal group Alliance Defending Freedom, which backs the school board.

For graphic on transgender rights and "bathroom bills", click: tmsnrt.rs/2l529J9