Donald Trump has been given the green light to ahead with plans to restrict military service for transgender men and women.
The US Supreme Court ruled in favour of the Trump administration on Tuesday, allowing the plan to progress as other legal challenges take place.
The high court split 5-4 in allowing the plan to take effect, with the court's five conservatives backing it and its four liberal members saying they would not have.
Its decision clears the way for the Pentagon to bar enlistment by people who have undergone a gender transition.
It will also allow the administration to require that military personnel serve as members of their biological gender unless they began a gender transition under less restrictive Obama administration rules.
The Trump administration has sought for more than a year to change the Obama-era rules and had urged the justices to take up cases about its transgender troop policy immediately, but the court declined for now.
Those cases will continue to move through lower courts and could eventually reach the Supreme Court again.
The fact that five justices were willing to allow the policy to take effect for now, however, makes it more likely the Trump administration's policy will ultimately be upheld.
Justice Department spokeswoman Kerri Kupec said the department was pleased with the court's decision.
"The Department of Defence has the authority to create and implement personnel policies it has determined are necessary to best defend our nation," she said, adding that lower court rulings had forced the military to"maintain a prior policy that poses a risk to military effectiveness and lethality".
Groups that sued over the Trump administration's policy said they ultimately hoped to win their lawsuits against the policy.
Jennifer Levi, an attorney for GLBTQ Legal Advocates & Defenders, said in a statement that the "Trump administration's cruel obsession with ridding our military of dedicated and capable service members because they happen to be transgender defies reason and cannot survive legal review".
Until a few years ago service members could be discharged from the military for being transgender. That changed under the Obama administration.
The military announced in 2016 that transgender people already serving in the military would be allowed to serve openly.
And the military set July 1, 2017, as the date when transgender individuals would be allowed to enlist.
But after President Donald Trump took office, the administration delayed the enlistment date, saying the issue needed further study.
And in late July 2017 the president tweeted that the government would not allow "Transgender individuals to serve in any capacity in the US Military".
He later directed the military to return to its policy before the Obama administration changes.