The LGBT rights organization the Human Rights Campaign (HRC) led the charge against President Donald Trump’s newly announced ban on transgender military service members Wednesday, calling it an “all out assault on service members.”

HRC said the ban would threaten more than 15,000 currently serving troops. Other estimates range from 4,000 to 6,000 members of the military.

The White House did not explain how the ban would be implemented, and whether all transgender service members will be immediately discharged. The Pentagon was referring inquiries to the White House on Wednesday.

The Civil and Human Rights Coalition’s president and CEO Vanita Gupta released a statement saying President Trump “attacked the brave and patriotic transgender Americans who are voluntarily serving in the military to protect our country and our freedoms. “

Aaron Belkin, the director of the Palm Center, which focuses on sexual minorities in the military, called the move a “shocking and ignorant attack on our military and on transgender troops who have been serving honorably and effectively for the past year.”

Blake Dremann was one of the first transgender service members to be promoted after the previous ban on transgender soldiers ended in 2016, and is the president of SPART*A, a LGBT military advocacy group. He said transgender military members have served for “over a year openly with no foreseeable impact to readiness or distraction to the overall mission.”

Iraq and Afghanistan Veterans of America founder and CEO Paul Reickoff tweeted his support for equality.

.@IAVA stands in support of #equality. Diversity makes our national security stronger. It’s just common sense. https://t.co/UGyCRPylGq

— Paul (PJ) Rieckhoff (@PaulRieckhoff) July 26, 2017

Trump’s policy announcement did find favor among conservative groups. The American Family Association released a statement saying it “applauds President Trump for his courageous decision to end the usage of our military for social engineering and political correctness.”

The American Civil Liberties Union appeared to be gearing up for a legal fight.

Thousands of trans service-members on the front lines deserve better from their commander-in-chief, @realDonaldTrump. Contact the ACLU. pic.twitter.com/tr9YroUrKo

— ACLU National (@ACLU) July 26, 2017

Many opponents of the president’s move cited a 2016 RAND Corporation assessment of the impact of transgender service members serving openly that estimated there are 1,320 to 6,630 out of 1.3 million active service members in total. The study estimated between 29 and 129 service members yearly would seek “transition-related care that could disrupt their ability to deploy.”

The report concluded there would be “little or no impact on unit cohesion, operational effectiveness, or readiness.”

Trump tweeted his plan to ban transgender soldiers on the 69th anniversary of the 1948 signing of President Harry Truman’s executive order abolishing racial segregation in the military.