Fitch Ratings said it is taking the action because state lawmakers failed to take any action to solve the state pension crisis.
The move could make it more expensive for the state to borrow money.
"It's like a mortgage," Rutherford said. "If you got a bad credit score, you're paying more on your mortgage. If you got a good credit score, you don't pay as much. This comes right out of the purses and wallets of the taxpayers of Illinois."
Fitch warned that further inaction on the pension crisis could lead to a damaging, downgrade of the state's credit rating.