A gender neutral sign is posted outside a bathroom at Oval Park Grill on May 11, 2016 in Durham, N.C. Ten more states filed a lawsuit against the Obama administration over its directive requiring schools to allow transgender students to use bathrooms that align with their gender identity. (Sara D. Davis/Getty Images)

Ten additional states are suing the Obama administration to stop a directive that requires schools to allow transgender students to use bathrooms aligned with their gender identity under the threat of losing federal funding, bringing the total number of states challenging the guidance to 21.

Nebraska Attorney General Doug Peterson announced the lawsuit, filed in federal court in Nebraska, on Friday afternoon. The state is joined by nine others: Arkansas, Kansas, Michigan, Montana, North Dakota, Ohio, South Carolina, South Dakota and Wyoming.

The Obama administration, via the departments of Education and Justice, issued guidance to schools in May directing them to allow transgender students to use bathrooms that align with their gender identity, a move that plunged the administration further into the debate over how schools and the public should accommodate transgender people.

Lawmakers, school administrators, parents and the courts have been arguing over the issue. Lesbian, gay, bisexual and transgender advocates say barring transgender people from the facilities that align with their gender identities is a violation of their civil rights that threatens their well-being. But those who support such rules say they are necessary to safeguard privacy and traditional values.

Peterson argued that the administration bypassed the necessary procedures to create new federal regulations, in this case regulations that apply to every public school in the nation. He said the Obama administration has twisted the meaning of Title IX, which bars sex discrimination in public schools, to give transgender students the right to use bathrooms of their choice.

“It impacts all schools in Nebraska when they redefine the word sex in Title IX and say, ‘If you don’t embrace the definition you risk losing federal funding,’” Peterson said. “To us, this was an example of an agency going beyond its authority and impacting the state.”

Peterson said school administrators in Nebraska had typically accommodated transgender students on a case-by-case basis, usually offering them unisex bathrooms. The guidance, he said, leaves it up to individual children to determine which bathroom they should use, taking discretion away from administrators and parents.

This is the second lawsuit brought by a group of states over the Obama administration’s move to expand the rights of transgender students. Eleven states, along with the Arizona Department of Education, filed a lawsuit in federal court in Texas two weeks after the guidance was issued, arguing that the administration had overstepped its authority.

Friday’s lawsuit is part of a recent spate of litigation about the issue. There are now legal challenges to the Obama administration’s directive pending in at least four federal appellate circuits, setting up the possibility that courts could diverge on the issue and lead the U.S. Supreme Court to weigh in.

Stanford law professor Jeffrey Fisher, co-director of the school’s Supreme Court Litigation Clinic, said the court is more likely to take up an issue if federal appellate courts come to different legal conclusions. But he said the high court often waits until lawsuits have the chance to percolate through the legal system so it has the benefit of the input from other jurisdictions.

“The fact that a particular issue is being litigated in several states across the country weighs in favor” of the Supreme Court stepping in, Fisher said.

The Court of Appeals for the 4th Circuit, based in Richmond, Va., is the highest court to issue a ruling on the matter. In April, the court sided with a transgender student suing a Virginia school board for banning him from the boys’ bathroom, saying his lawsuit challenging that policy could move forward in a lower court. In its ruling, the appeals court deferred to the Obama administration’s position that Title IX protects the rights of transgender students to use bathrooms in accordance with their gender identity.

The school board, in Gloucester, Va., has fought to keep the student, who was born female but now identifies as a boy, from using the boys’ bathroom and hopes to take the case to the U.S. Supreme Court.

This week, Texas Attorney General Ken Paxton asked a federal court to allow localities to ignore the Obama administration’s guidance while the lawsuit filed on behalf of 11 states proceeds in Texas, hoping to stop it in its tracks before school starts in the fall.

In an appearance in Washington on Thursday, Paxton leveled sharp criticism against the directive on transgender students, calling it a “gun to the head” that threatens the independence of school districts to handle the issue as they see fit.

This story has been updated.