(Reuters) - An Indianapolis woman has sued the city's police department, contending that an order to remove an "Unmarked Police Car" bumper sticker from her minivan violated her rights to free speech, the group representing her said on Monday.

A lawsuit filed by the American Civil Liberties Union of Indiana on Friday argued that Indianapolis police did not have the right to question and make demands of Pamela Konchinsky after pulling over her vehicle earlier this month.

"We contend that the police officers who detained and interrogated our client without legal grounds to do so violated her constitutional rights," ACLU attorney Kelly Eskew said in a statement. "The promise of our Constitution is that these lines cannot be crossed."

According to the complaint, Indianapolis police officers told Konchinsky the bumper sticker would make people think she was impersonating a police officer and could get her shot, before demanding that she remove it from her rear window.

The suit was filed in the U.S. District Court for the Southern District of Indiana.

Indianapolis Metropolitan Police Department spokesman Lieutenant Chris Bailey said the department did not comment on pending litigation.

(Reporting by Jonathan Kaminsky in New Orleans; Editing by Peter Cooney)