The protests came just hours after Trump announced the ban on Twitter.
"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," tweeted the president, who said on the campaign trail that he supported the rights of LGBTQ Americans. "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."
The president did not specify what the ban would mean for currently serving transgender soldiers.
Below, a round-up of the protests across the country.
NEW YORK CITY
Hundreds of protesters, many carrying signs that read "Resist!" descended upon the U.S. Armed Forces recruiting station in Times Square to denounce the ban.
Demonstrator Yael Leberman told The Associated Press that transgender people "are completely adequate to serve" and combat is "not about physical, it's about mental" abilities.
Protesters assembled in at least two locations in San Francisco Wednesday evening to speak out against the ban.
Several hundred protesters gathered at the city’s Harvey Milk Plaza -- named after the gay rights icon and the country’s first openly gay elected official -- and urged those in attendance to “stand up” and “fight back."
Some demonstrators waved pink and blue flags, while others held signs that read "trans lives are not a burden" and "Resist."
Protesters, including transgender veterans, gathered at the Los Angeles LGBT Center in Hollywood. Some carried signs that read "Proud Trans Vet" and "LGBT Solidarity."
"There are people who are retiring in the military, there are people who've done 18, 19 years and are about to retire and now it's all taken away from them," five-year military veteran Rudy Akbarian, 27, told The Associated Press. "It's not fair."
The ACLU of Southern California says it will sue the Trump administration to stop the ban if it actually becomes policy.
More than a hundred people gathered at the White House, including some transgender service members and veterans who said they were "shocked and angry” when they first heard about the ban.
"I was actually really shocked and angry, I don’t know how he came to that conclusion so fast,” Kara Zajac, a transgender woman and a navy veteran, told ABC affiliate WJLA.
“The previous administration came up with a sensible plan for allowing transgender people to openly serve and that plan needs to be openly respected,” Raffi Freedman-Gurspan, Director of External Relations for the National Center for Transgender Equality, told the crowd.