Backers of a plan to change Illinois' income tax structure say they've collected more than 150,000 signatures from supporters.

The (Springfield) State Journal-Register reports that members of the group A Better Illinois say they hope to keep collecting signatures on their petition through the spring. They want to convince lawmakers to put a constitutional amendment on the 2014 ballot. The amendment would allow the state to adopt a graduated or "progressive" tax.

Under a graduated tax, higher earners pay a larger percentage of their income than middle and lower-class taxpayers. It's similar to the federal income tax structure.

Illinois' Constitution currently requires a flat income tax. Changing it would require a three-fifths vote in the Legislature and approval by voters.

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