Governor Bruce Rauner is predicting companies would flee the state if Illinois changed its income tax structure.
Currently the personal income tax rate is 3.75 percent.
Some Democratic candidates for governor are starting to campaign on changing to a graduated income tax rate - so wealthy people pay more.
Rauner says that proposal would result in business owners leaving Illinois.
If we double their tax rate, which could happen under some sort of a graduated scheme, we’ll see the flood of businesses go to a torrent out of Illinois.
State senators had been debating whether to increase the flat tax rate to nearly 5 percent as part of a grand bargain to end the budget impasse.
But negotiations over that plan have stalled.
For Illinois to move to a graduated income tax, the state constitution would have to be amended.