CHICAGO (CBS) — The Illinois General Assembly got an early start on a plan to try to keep Chicago’s two financial exchange companies in the state Monday, just ahead of today’s opening of the fall veto session.

As WBBM Newsradio’s David Roe reports, the legislation proposed by Illinois Senate President John Cullerton (D-Chicago) calls for a 50 percent cut in the state corporate income tax bills for the CME Group and CBOE Holdings.

LISTEN: WBBM Newsradio’s David Roe reports

Crain’s Chicago Business reports the exchanges would only have to pay corporate income tax on 27.54 percent on receipts from electronic transactions.

The old-fashioned open outcry transactions on the trading floor would still be subject to 100 percent income tax, but those transactions now constitute a minority of the business at the exchanges, Crain’s reported.

While Gov. Pat Quinn and House Democrats have come out in support of a deal to keep the exchanges in Illinois, it is not clear whether they will back Cullerton’s bill, Crain’s reported.

Both the CME Group and CBOE have threatened to leave Illinois over tax hike approved this year, which jacked the corporate income tax up from 7.3 to 9.5 percent.

CME Group executive chairman Terrence Duffy said in June that the firm would lose about $50 million this year from the tax hike.