National Nurses United says on Wednesday the group will outline a legal challenge to the city's demand.
"We think it's outrageous that at the eleventh hour, the city has decided to change a permit that had already been granted," said Jan Rodolfo, Midwest director, National Nurses United.
The flyers had been printed and the musical act booked. But on Tuesday National Nurses United received a letter from the city saying the rally's expected crowd would likely exceed 5,000, the capacity of Daley Plaza, because of a planned concert by Libertyville-native Tom Morello of the band Rage Against the Machine.
Instead, the city proposed an alternative location, the Petrillo Band Shell, which can hold larger crowds.
"Chicago is a world class city," said Rodolof. "You can't imagine the mayor of London canceling a demonstration because it's greater than 2,000. It shouldn't be happening here."
With summit weekend now just 10 days away, crews began removing large trash cans from downtown Tuesday for security reasons, replacing them with wire receptacles that are more see-through.
On Tuesday night, the NATO host committee held its final informational meeting with businesses.
"It sounds intimidating, upwards of a hundred motorcades, but not every motorcade will be President Obama's motorcade," said Special Agent In Charge Frank Benedetto, U.S. Secret Service.
"Uncertainty exists about how much traffic is going to be there, even though we're allowed to come in and out," said Bonnie Sanchez-Carlson, Near South Planning Board.
Though committee members suggest those living or working near McCormick Place carry identification, they disagree with companies that have advised employees not to wear business suits to blend in with potential protesters.
"Come to work like you come to work. Dress like you dress every day," said Arnette Heintze, security consultant.
With hotels filling up, Occupy Chicago has put out a call for volunteer housing.
Terry Keenan plans to open his Lincoln Square home and yard to dozens of out of town protesters.
"It will be a kind of a welcoming place, just a bunch of friends in the neighborhood coming over. Not anything to be nervous about," said Keenan.