SPRINGFIELD – Illinois probably will enact an 18 percent expansion of the Medicaid program in 2014, with the federal government paying almost the entire bill for the first three years as part of the Affordable Care Act.

But the expansion, which is expected to add about 500,000 people to a program that already covers 2.7 million of the state’s 12.8 million residents, may not come without vigorous debates in the Illinois House and Senate, lawmakers said last week.

Votes could come as soon as the fall veto session, House Majority Leader Barbara Flynn Currie said, though it’s unclear whether the expansion requires legislative approval.