SPRINGFIELD — A game of legislative chicken over pension reform moved into its second week Wednesday when a Senate panel endorsed a union-backed proposal designed to repair the state's broken retirement systems.

The plan, which now heads to the full Senate for further debate, is competing for support with a separate blueprint that has already moved out of the House, setting up a showdown between the top two Democrats in the General Assembly.

Senate President John Cullerton believes the plan that emerged from the Senate Executive Committee on a 10-5 party-line vote Wednesday afternoon is the only one that would survive a court challenge.

But House Speaker Michael Madigan also believes the proposal he muscled through the House last week will survive a constitutional test.

The coalition of unions backing Cullerton's plan made it clear to members of the committee that they weren't ready to compromise.

Illinois AFL-CIO President Michael Carrigan of Decatur threatened to withdraw the union's backing of Cullerton's legislation if any changes are made to the legislation.

"We cannot ignore the Illinois Constitution. We believe this legislation in its present form represents a fair, responsible and constitutional solution," Carrigan said.

"We are committed to this agreement," Illinois Federation of Teachers President Dan Montgomery added.

Cullerton says his plan is constitutional because employees and retirees would be given a series of choices of whether to accept lower cost-of-living increases or take state-funded health insurances.

By contrast, the plan that won narrow approval in the House last week calls for employees to work longer, pay more toward their retirement plans and receive reduced cost-of-living adjustments.

In addition to the constitutional concerns, there is a wide savings gap between the two plans. The union-supported measure would save an estimated $46 billion over three decades, while Madigan's plan would save more than $140 billion over 30 years and would fully fund the pension retirement systems.

Republicans were skeptical that the Cullerton measure would be the final word on fixing a pension system that is more than $96 billion out of whack.

"When you say 'once and for all,' that's a long time," Sen. Dave Luechtefeld, R-Okawville, said.

The Illinois Retired Teachers Association said it will sue if the plan is adopted.

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Bob Pinkerton of Jacksonville, vice president of the organization, said the choices being offered fall short.

"A choice of either jump off a cliff or I'll shoot you is not really a choice," Pinkerton said.

In addition to a possible Senate vote on the Cullerton plan on Thursday, Madigan is scheduled to launch talks with school management lobbyists on a plan to shift the cost of pensions from the state to local school districts.

Republicans have fought the so-called "cost shift" since it was floated by Madigan last year, saying it could lead to higher local property taxes.

The legislation is Senate Bill 2404.