CHICAGO (AP) — A group aligned with the Republican Party has filed a lawsuit challenging the language of a proposed Illinois constitutional amendment that creates a graduated-rate income tax.

The Illinois Policy Institute contends in the lawsuit filed Monday in Cook County Circuit Court that the explanation of the amendment on the ballot for voter approval is misleading and needs court-ordered clarification.

The Illinois General Assembly in May approved the language in the proposed amendment that is atop the Nov. 3 ballot explaining the pros and cons of adding a graduated rate to the income tax system.

The Vote Yes for Fairness group that backs the amendment calls the lawsuit “frivolous.”