File photo of US soldiers. (Getty)

Transgender soldiers could be denied entry into the US military unless the Pentagon moves to fully implement a pro-equality measure passed last year by Barack Obama.

According to a Military Times report on Thursday, Jim Mattis – Donald Trump’s Defense Secretary – could decide to block the order. It is “unclear” what he will decide, the paper reported.

In June of last year, President Obama asked the Pentagon to lift its long-held ban on transgender soldiers serving openly in the military.

Obama’s ruling meant, in theory, that transgender soldiers would be afforded the same healthcare coverage as other soldiers – including, if required, hormone therapy and gender reassignment surgery.

The Department of Defense was given until July 1st of this year to implement the policy, with LGBT advocates hopeful that transgender soldiers would be able to serve openly in just less than a month.

Last month, Defense Secretary Mattis distributed a carefully worded memo saying that Obama’s pro-trans plans would proceed “unless they cause readiness problems that could lessen our ability to fight, survive, and win on the battlefield”.

But now senior leaders within each of the military services are voicing “lingering concerns” about the Obama policy, the Military Times reports. These doubts could delay the implementation of Obama’s order.

Some in the military have criticised Obama’s pro-trans policy as “social experimentation”.

It is estimated that some 7,000 members of the US military’s 1.3 million active duty members are transgender.

President Donald Trump has not said much publically on the issue of transgender soldiers, but his decision earlier this year to revoke Obama’s guidelines on gender-neutral bathrooms left many advocates of transgender rights frightened.

The Army and the Marine Corps are the most vocal in pushing for a delay, according to the Military Times.

One military official speaking to the paper anonymously said that no firm decision has been reached.

Until Obama’s decision last year, the US military banned transgender soldiers from serving under medical regulations with disqualified people from service if they have “curre

nt or history of psychosexual conditions, including but not limited to transsexualism, exhibitionism, transvestism, voyeurism, and other paraphilias”.

Obama’s decision to lift the ban last year came six years after the US Congress overturned the long-held ‘Don’t Ask Don’t Tell’ rule, which banned gay and lesbian soldiers from being open about their sexuality.

Every Democratic member of the Senate voted to overturn the ‘Don’t Ask Don’t Tell’ rule in 2010, whilst all but two Republicans voted to keep it in place.