President Donald Trump has announced plans to ban transgender people from serving in the U.S. military in any capacity, The Washington Post reports.

The move reverses former President Barack Obama’s decision that would have allowed them to openly serve. Trump said the decision comes from the need to focus on victory, and that the military cannot accept the burden of higher medical costs and “disruption” caused by transgender troops.

“After consultation with my Generals and military experts, please be advised that the United States Government will not accept or allow transgender individuals to serve in any capacity in the U.S. Military,” Trump tweeted. “Our military must be focused on decisive and overwhelming victory and cannot be burdened with the tremendous medical costs and disruption that transgenders in the military would entail.”

The announcement follows defense secretary, Jim Mattis’, decision to delay the implementation of a plan that would allow transgender troops to serve by six months. The Joint Chiefs of Staff requested the delay, and allows for further review of how allowing transgender recruits to serve would affect the military’s lethality.

“Since becoming the 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 force?” Mattis said last month in a statement. “Put another way, how will the decision affect the ability of America’s military to defend the nation? It is against this standard that I provide the following guidance on the way forward in accessing transgender individuals into the military Services.”

Currently, thousands of troops in the military identify as transgender, and estimates as high as 11,000 are in the reserves and active duty military, according to a study released by the Defense Department.