The Pentagon on Friday said that it was delaying by six months implementation of a policy that allows openly transgender people to enlist in the U.S. armed forces.

The policy was set to take effect Saturday, July 1.

The military service chiefs asked for the delay and Defense Secretary James Mattis reportedly agreed.

Former Defense Secretary Ashton Carter last year lifted the ban on openly transgender military service. The policy change came after a year-long review.

In a memo released last week, Mattis said that his concerns about transgender enlistments had to do with military readiness.

“Since becoming Secretary of Defense, I have emphasized that the Department of Defense must measure each policy decision against one critical standard: will the decision affect the readiness and lethality of the armed forces?” Mattis wrote. “Put another way, how will the decision affect the ability of America’s military forces to defend the Nation?”

The Human Rights Campaign (HRC), the nation's largest LGBT rights advocate, called the delay “needless.”

“Once this important policy is implemented, it will strengthen our military by allowing qualified and talented transgender people to enlist or commission,” said HRC National Press Secretary Stephen Peters, a Marine veteran discharged under Don’t Ask, Don’t Tell. “Each day that passes without the policy in place restricts the armed forces’ ability to recruit the best and the brightest, regardless of gender identity. We are disappointed in this needless delay because the thousands of highly trained and qualified transgender service members openly and proudly serving our nation today have proven that what matters is the ability to accomplish the mission, not their gender identity.”