The Pentagon on Friday said that it will allow transgender troops currently serving in the U.S. military to re-enlist as it studies the issue.

In a memo to top military leaders, Defense Secretary Jim Mattis wrote that he wants “to emphasize that the current policy and procedures remain in place.”

“Transgender service members whose term of service expires while the interim guidance is in effect, may, at the service member's request, re-enlist under existing procedures,” Mattis said.

He added that while this is the current policy, it only remains in effect until the Pentagon implements its “final policy concerning the military service by transgender individuals.”

Last month, the White House issued guidance on implementing President Donald Trump's ban on transgender troops, which he first announced on Twitter.

The Trump administration's guidance directs the military to bar transgender people from entering the military and to stop paying for the transition-related health care of active duty transgender troops, but stops short of banning transgender troops, leaving the decision of what the military should do about active-duty transgender troops to military leaders.

The Pentagon is expected to deliver an implementation plan to the administration no later than February 21.

Mattis' memo was released on the same day that New York Senator Kirsten Gillibrand, a Democrat, introduced a bipartisan bill in the Senate that would block Trump's effort to bar transgender people from military service.

(Related: John McCain co-sponsors bill which seeks to block Trump's ban on transgender troops.)