The Pentagon said on Friday it was reviewing recommendations from the US military chiefs that included calls for more time to implement plans to allow new transgender recruits to join the US armed forces.
Pentagon spokeswoman Dana White said no decision on the matter had been made yet.
"Different services had different takes. So, some asked for time," she said.
The Pentagon ended its ban on openly transgender people serving in the US military in 2016 under the Obama administration. It was expected to also start allowing transgender individuals to begin enlisting this year, provided they had been "stable" in their preferred gender for 18 months.
News of a potential delay under President Donald Trump's administration alarmed transgender advocates.
"There are thousands of transgender service members openly and proudly serving our nation today ... what matters is the ability to get the job done — not their gender identity," said Stephen Peters of the Human Rights Campaign.
Last year, then-Defense Secretary Ash Carter cited a study by the RAND Corporation saying there were about 2,500 transgender active-duty service members and 1,500 reserve transgender service members.
Rand's figures were within a range, which at the upper end reached 7,000 active duty forces and 4,000 reserves.