U.S. President Donald Trump looks up during a meeting about healthcare at the White House in Washington, U.S., March 13, 2017. REUTERS/Kevin Lamarque

President Donald Trump said Wednesday that his administration will block transgender people from serving in the U.S. military.

Trump made the announcement, which would represent a major shift in military policy, on Twitter. It reverses an Obama administration policy announced last year. Trump said he had made the decision after consulting 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 transgender in the military would entail. Thank you”

It’s uncertain how this would affect openly transgender people currently serving in the U.S. military. Up to 10,700 transgender people may already be serving in the US military, according to a 2016 study by the RAND Corporation.