Pritzker and Democratic state legislators who back a graduated income tax hope to act on the issue before the General Assembly adjourns at the end of May. Lawmakers would need to pass a bill setting new tax rates, and three-fifths majorities in each chamber would have to approve an amendment doing away with the state constitution’s flat tax requirement. Before any of that could take effect, voters would have to approve the amendment, which can’t happen until November 2020 at the earliest.