American President Donald Trump has banned transgender people serving in the US military.
His announcement was made on his Twitter account on Wednesday.
He 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."
There have been protests across New York City, Washington, DC and San Francisco since the announcement was made.
What does transgender mean?
According to the charity Stonewall, transgender is a word that describes people whose gender is not the same as, or does not sit comfortably with, the sex they were born as.
For example, a transgender man would have been described as girl at birth but lives as a male.
A transgender woman would be described as a boy at birth but lives as a female.
Transgender people often find it important to appear to others how they feel inside.
This can involve dressing in certain clothes or asking to be described in a certain way.
Some people choose to have medical procedures to alter their appearance.
"Not all trans people want or are able to have this [medical treatment]," say Stonewall.
This medication comes at a cost and healthcare isn't free in America.
Why did President Trump make this decision?
Many transgender people are currently serving in the US military. Thanks to a rule made by previous president Barack Obama, the US government was willing to pay their medical costs.
President Trump thinks that the US government should not be responsible for this and the money should be spent on something else.
However, the president's political party has previously campaigned against rights for transgender people.
During the election in 2016, the party had two policies which clearly opposed laws in favour of transgender people.
One law allowing people to use certain public toilets was described as "illegal and dangerous".
The US military spends $6.2 billion (£4.7 billion) on healthcare for people in the army, navy, air force and marines.
A research company in America believes that only 0.13% of that money is spent on transgender service personnel - that's $8.4 million (£6.4 million).
That same company, Rand, also says that there are about 4,000 US active-duty and reserve service members who are transgender. However, some campaigners say the figure is higher than 10,000.
How will people be affected?
At the moment, it's not clear how people already in the military will be affected by the ban.
The people who work with Donald Trump to govern America have not put together a plan of how this ban will work.
What has the reaction been?
Some people agree with President Trump and think the money should be better spent on other things.
However, some groups and campaigners believe that Mr Trump's decision is wrong and unfair.
They also believe that the reason for his decision - saving money - is not good enough as they think the American government spends money on many other things that could easily be cut instead.
What are the UK rules?
Transgender people are allowed to serve in the UK military and a lot of army officials have spoken out about President Trump's ban.
A spokesman from the Ministry of Defence told the BBC: "We are clear that all members of our armed forces play a vital role in keeping our nation safe. We will continue to welcome people from a diverse range of backgrounds, including transgender personnel."