The bill passed the state House of Representatives in March 2011. Emanuel said Chicago's homicide rate is up and the city clearly needs more legal tools to act against gangs, the Chicago Sun-Times reported.
Police statistics show there were 120 killings in the city in the first three months of 2012, up from 75 a year earlier.
"We cannot fight criminal gang violence alone and need additional tools to go after gangs in our city and throughout Illinois," Emanuel told Senate President John Cullerton, a Chicago Democrat, in a March 30 letter.
Under the bill, participants in gang crimes, including violence, drug and weapons crimes and illegal debt collection, could be prosecuted under the racketeering law and subject to penalties of 10 to 30 years in prison. Legislators have reduced its scope so that it no longer covers government corruption and other white-collar crimes.