The reason is the Trump administration's decision to take federal control over the US capital's police force and deploy the national guard – without the consent of the local government.
According to the lawsuit, which has been filed by Washington DC lawyer Brian Schwalb, national guards are patrolling the city's streets and carrying out both searches and arrests. This despite federal laws that generally prohibit the military from acting as local police.
"Using the national guard to conduct law enforcement is not only unnecessary and unwanted, it is also dangerous and harmful to the city and its residents," says Schwalb in a statement.
"It's DC today but it could be any other city tomorrow. We're doing this to put a stop to this illegal federal overreach."
It was on August 11 that Donald Trump declared a "state of emergency" in Washington DC, which he then also called a "crime-infested rat hole". The other day, Trump said that they also intend to deploy the national guard in "hell" Chicago.