CHICAGO (CBS) — After learning their protest rally could be much larger than originally anticipated, city officials have told National Nurses United that they must change the route of their march on the weekend of the NATO summit to avoid the Loop.

Chicago Law Department spokesman Roderick Drew confirmed the city has modified the nurses’ protest permit to move their rally on the Friday before the NATO summit from Daley Plaza to Grant Park.

The nurses group was furious with the change, calling it an attempt to “quarantine a long-planned rally.” They are planning a protest at City Hall on Wednesday to discuss filing a legal challenge to the city’s changes to their march route.

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Originally, the city had approved a march route that would go from the Sheraton Chicago Hotel & Tower to Daley Plaza, and organizers had said they were expecting about 1,000 protesters. The protesters planned to gather at the hotel — where President Barack Obama will be staying during the NATO summit — at 10 a.m., followed by an 11 a.m. protest march to Daley Plaza. Now they must go to Grant Park instead.

The original route would have taken protesters from the hotel at Columbus Drive and North Water Street, north to Illinois Street, west to Michigan Avenue, south to Wacker Drive, west to State Street, south to Randolph Street, then west to Dearborn Street and into Daley Plaza.

The new route will instead take the protesters south on Michigan Avenue, all the way to Monroe Drive, and east into Grant Park, at Butler Field. The date and time of the march will not be changed. The protest must wrap up by 1 p.m.

Drew said the city changed the march route because officials believe the protest will draw significantly more people than protesters originally estimated, given an aggressive ad campaign that included posters on the CTA, and that the group has enlisted musician Tom Morello — a prominent activist and guitarist for the band Rage Against The Machine — to play during their rally.

“For all of these reasons, they have modified the permit to put the group in Grant Park,” Drew said.

Registered nurse Jan Rodolfo said, “We’re feeling outraged. We think they’re trying to block our message from getting out. … Nurses don’t hurt people, we heal people. … If 2,000 nurses and Tom Morello playing acoustic guitar are a security threat, we’ve got a real problem.”

The group will be allowed to use the Petrillo Music Shell in Grant Park for Morello’s musical performance.

“Apparently the mayor thinks nurses and Tom Morello are a national security threat,” said NNU Executive Director RoseAnn DeMoro. “How shameful for this last minute attempt to squelch this event – especially given that the G-8 leaders have long since decided to flee from the public view rather than hear our voices.”

The nurses originally scheduled their protest when the upcoming G8 summit was still planned to be held in Chicago on the same weekend as the NATO summit. They decided to continue with their rally even after the G8 summit was moved to Camp David. The group is pushing for what it calls a “Robin Hood tax” on Wall Street to raise money “to heal the U.S. and global economies.”

“With this blatant effort to stifle dissent, Mayor [Rahm] Emanuel is exposing the city and our country to international ridicule and embarrassment. Is it really worth doing so just to please the Chicago Board of Trade, Mercantile Exchange and other Wall Street interests?” DeMoro said.