A spokeswoman for the Justice Department, Dena W. Iverson, said the department was disappointed with the decision and was reviewing its options.  In a statement, several civil rights organizations that had submitted a brief opposing the injunction called the ruling unfortunate and premature.  “A ruling by a single judge in one circuit cannot and does not undo the years of clear legal precedent nationwide establishing that transgender students have the right to go to school without being singled out for discrimination,” the groups — Lambda Legal; the American Civil Liberties Union and the A.C.L.U. of Texas; the National Center for Lesbian Rights; the Transgender Law Center; and G.L.B.T.Q. Legal Advocates & Defenders — said in their statement.  The ultimate impact of the Texas decision is unclear and is likely to be limited, legal experts said. For one thing, more senior courts in other regions have agreed with the administration that transgender students and workers are protected by existing laws against sex discrimination, and their decisions will not be altered by the Texas ruling.  Also, the decision will not necessarily affect the outcome of other current cases. In the most prominent one, a federal court in North Carolina is weighing almost identical issues in suits brought by civil rights groups and the Justice Department that seek to block a state law requiring people in government buildings, including public schools, to use bathrooms that correspond to the gender on their birth certificates.  Adding another major note of uncertainty, the United States Supreme Court has temporarily blocked a decision by the Fourth Circuit Court of Appeals that required a school district in Virginia to allow a transgender boy to use the boys’ bathrooms. The Supreme Court issued a temporary injunction until it decides, probably this fall, whether to hear the case.  If the Supreme Court does take the case and reaches a majority decision one way or another, then existing rulings by district and appeals courts could be superseded. If the Supreme Court takes the Virginia case but then is divided, four to four, on the issues, the Fourth Circuit’s existing decision in favor of transgender rights would take effect, although it would not be a nationally binding precedent.  The Texas lawsuit, filed by Mr. Paxton on behalf of officials in 13 states, argued that the Obama administration had overstepped its authority in a series of pronouncements in recent years holding that discrimination against transgender people is a violation of existing laws against sex discrimination, including Title IX in federal education laws and Title VII in federal civil rights laws governing the workplace.  In May, in the latest such statement, the federal Justice and Education Departments issued a letter to public schools stating that transgender people should be free to use bathrooms and locker rooms that match their gender identities, and that schools that refused could lose federal funds.  “A school may not require transgender students to use facilities inconsistent with their gender identity or to use individual-user facilities when other students are not required to do so,” the letter stated.  The letter was quickly condemned by social conservatives, leading numerous state governments and school districts around the country to file lawsuits seeking to prevent the administration from taking action.  The Obama administration, seeking to deflect the Texas lawsuit and another brought by 10 other states, argued that the directive was not a regulation or mandate but rather an explanation of how the administration interpreted existing sex-discrimination protections. But it carried a threat that the administration might sue noncompliant school districts and seek to cut off vital federal education aid.  The states argued not only that the administration was wrong as a matter of law, but also that it had failed to follow legal procedures for issuing what the states called a “new mandate” that “harms school districts from coast to coast by usurping lawful authority” and jeopardizing “billions of dollars in federal funding.”  The Justice Department countered that the case was not suitable for litigation because the states had not shown evidence that they faced imminent harm, let alone a likelihood of success on the merits.  If the administration brought action against school districts, the government and groups supporting lesbian, gay, bisexual and transgender rights argued, the school districts or states could make their case in court.  “There is a multistep procedure before a state might lose federal funding,” said Jon W. Davidson, the legal director of Lambda Legal. “The government would have to specifically challenge a state, the state could respond, the government could bring a lawsuit, and then litigation in the courts would decide whether the government’s interpretation of the law is correct or not.”  Follow Erik Eckholm on Twitter: @eckholm.  Follow Alan Blinder on Twitter: @alanblinder.  For breaking news and in-depth reporting, follow @NYTNational.  A version of this article appears in print on August 23, 2016, on page A15 of the New York edition with the headline: Judge Halts Obama Push on Transgender Access. Order Reprints| Today's Paper|Subscribe
A judge in Texas said the Obama administration had not followed federal law in an attempt to expand bathroom access for transgender students.