The American Civil Liberties Union of Illinois is suing the City of Chicago, alleging unequal police deployment to minority neighborhoods.

The lawsuit filed Thursday claims the number of police in predominantly African American and Hispanic communities is disproportionately low as measured by the number of emergency calls made in those neighborhoods. As a result, the ACLU said those areas experience slower response to 911 calls than that of predominantly white neighborhoods.

ACLU legal director Harvey Grossman said the organization has long been stonewalled by the city in its efforts to gather police deployment statistics. He cited recent news reports from the Sun-Times and the Chicago News Cooperative that measured emergency response times in some city neighborhoods as the basis for the suit. The ACLU wants the city to end its current method of police deployment and submit “a plan that will guarantee that all neighborhoods receive equal emergency services.”

“Tell the city what you’re doing and why you’re doing it,” said Grossman. “Put the numbers out there. Tell us why you’re making the decisions, and let us all assess the equality and fairness of it.”

Chicago Mayor Rahm Emanuel defended the city’s police deployment at a press conference on Thursday. He said the city is still using crime statistics to better determine where to deploy police officers.

The police department did not immediately respond to calls for comment.