It cost the department $35,000 this year and last to clean up feathers and other debris, public works spokeswoman Christine Falvey said. The event is now in its fifth year, she said.
Falvey said the department appreciates the spirit behind the pillow fight and doesn't want to see it shut down, but believes organizers need to be more responsible.
The department is asking those behind the event to apply for a permit and provide cleanup, security and portable toilets. Falvey said trash cans are also important.
"If you just show up at a random place and there are no receptacles and a large crowd, there's obviously going to be litter afterward," she said.
The $35,000 price tag is for the hours employees spent on cleanup, Falvey said.
"These are crews that are meant to keep downtown clean," she said.
"They're called away from what they're usually doing to clean up all these feathers."
The department has not yet been able to identify the organizers of the pillow fight and is considering forwarding a complaint to the city attorney's office.