Massachusetts Attorney General Maura Healey led a group of 15 attorneys general in filing a court brief on Monday opposing President Donald Trump's ban on transgender people serving openly in the U.S. military.

The attorneys general wrote in their brief that they support the rights of transgender people "to live with dignity, to be free from discrimination, and to participate fully and equally in all aspects of civic life."

Trump banned transgender individuals from serving openly, saying they would increase medical costs and hurt troop readiness, effectiveness and unit cohesion.

The attorneys general filed an amicus brief in a lawsuit opposing the ban, Jane Doe vs. Donald Trump, brought in the U.S. District Court for the District of Columbia by two gay rights groups.

According to the court brief, approximately 150,000 veterans, service members and National Guard members identify as transgender, and transgender individuals volunteer to serve at twice the rate of adults in the general population.

"Nothing about being transgender inhibits a person's ability to serve in the military or otherwise contribute to society," they wrote.

They point to studies showing that letting transgender people serve has no impact on military readiness. They note that countries including Australia, Britain, Canada and others allow transgender individuals to serve.

Transgender individuals have been allowed to serve openly in the military since June 30, 2016, due to a policy shift under the Obama administration. Trump, a Republican, changed the policy in July.

Healey, a Democrat who is gay, has been a strong defender of gay and transgender rights. She has also taken a strong stance against many of Trump's decisions, joining or leading lawsuits related to Trump's policies on immigration, health care and other issues.

Also signing onto the brief are the attorneys general of California, Connecticut, Delaware, Hawaii, Iowa, Illinois, Maryland, New Mexico, New York, Oregon, Pennsylvania, Vermont, Rhode Island and the District of Columbia.