The Republican governor last week launched a financial probe of the nation's third-largest public school system through the Illinois State Board of Education. Rauner said the board has the legal authority to block borrowings by districts found to be in financial duress.

"The state board has never chosen to do that for the city of Chicago. I hope that never becomes necessary. But we've got to be ready to take action," Rauner told reporters.

CPS officials could not immediately be reached for comment.

CPS is struggling with a $1.1 billion structural budget deficit, caused largely by escalating annual pension payments that will reach $676 million this fiscal year. The district's efforts to gain an additional $480 million in state dollars to pay its pension bill have become entangled in an ongoing impasse between Rauner and Democrats who control the legislature.

To keep operating in anticipation of $1 billion in property tax revenue next month, CPS turned to short-term borrowing and a $725 million bond sale earlier this month for cash flow. The district said it plans to seek additional short-term borrowing authority from its governing board in the future.

Rauner said accusations by Chicago officials that he attempted to derail the Feb. 3 bond sale by pushing for a state takeover or possible bankruptcy for CPS were "completely false."

Skittish investors demanded hefty yields for the "junk"-rated bonds, which will cost the district nearly $1.9 billion to pay off by 2044.