(CNN) The American Civil Liberties Union on Thursday filed a lawsuit against the city of Philadelphia on behalf of the Poor People's Economic Human Rights Campaign after the progressive social justice group was denied a permit to protest the Democratic National Convention.
"We have a whole history of nonviolent, orderly and very large marches," PPEHCR national organizer Cheri Honkala told CNN. "We were devastated (by the city's decision) and had no other recourse."
An estimated 500 people are seeking to march "from City Hall to the doorstep of the DNC" under the PPEHRC banner -- part of a demonstration scheduled to coincide with the opening of the convention on July 25 at the Wells Fargo Center.
The ACLU is already representing a number of groups in litigation against Cleveland, alleging that the Republican convention host city's security procedures are set up to infringe on demonstrators' free speech protections. Both conventions, which take place on consecutive weeks beginning July 18, are expecting heavy protest activities and have come under criticism for trying to effectively cordon off the events from dissenting voices.
In the complaint delivered today, the ACLU argued that the city's "blanket ban" on rush hour marches will "violate PPEHRC's right to free expression under the First Amendment," noting that the group peacefully protested the 2000 GOP convention while walking the same route it sought for July.
A spokeswoman for Philadelphia Mayor Jim Kenney said the city's law department is "still reviewing the complaint" and had no other comment on its merits.
In a letter to Kenney's office a day earlier, the ACLU expressed concerns about a possible crackdown on protesters, saying it had become "deeply troubled by recent statements made by your attorneys that seem to be setting up the city for conflict."
Honkala, the Green Party's vice presidential nominee in 2012, said the PPEHRC reached out to ACLU lawyers more than a month ago and spent the last two weeks drafting the lawsuit.
"We're a little different because we're not saying things (in the Democratic party) should be fixed," she said Thursday. "We're advocating that people leave in droves."
The Democratic National Committee, which chose Philadelphia in February 2015 to host its quadrennial national convention, did not immediately respond to CNN's request for comment.