The US House of Representatives has voted to block President Donald Trump's military transgender ban from remaining in effect.
The Democratic-controlled House of Representatives has voted to block US President Donald Trump's move to restrict transgender men and women from military service.
The House passed, by a 243-183 vote, an amendment to block Trump's transgender ban from remaining in effect.
The move still faces an uphill battle and a Trump veto threat against the underlying $US1 trillion ($A1.5 trillion) spending bill, which includes the military budget.
The Trump administration's policy bars people who have undergone gender transition from enlisting.
It also requires military personnel to serve as their biological gender unless they began a gender transition under less restrictive Obama administration rules.
The policy is being challenged in court.
Under the Obama administration, the Pentagon announced that transgender people already serving in the military would be allowed to serve openly.
Trump reversed that policy beginning in 2017 with a tweet that the government would not allow transgender individuals to serve in any capacity in the military.
An estimated 14,700 troops on active duty and in the reserves identify as transgender, but not all seek treatment.
All four service chiefs told Congress last year that they had seen no discipline, morale or unit readiness problems with transgender troops serving openly in the military.
But they also acknowledged that some commanders were spending a lot of time with transgender individuals who were working through medical requirements and other transition issues.