SPRINGFIELD — A coalition of labor unions Tuesday filed the latest lawsuit seeking to torpedo the state's new pension law.

The We Are One coalition's lawsuit, filed in Sangamon County Circuit Court, is the fourth to be filed in connection with the retirement system changes approved by lawmakers and Gov. Pat Quinn in December.

"Our suit makes clear that pension theft is not only unfair, it's clearly unconstitutional," said Illinois AFL-CIO President Michael T. Carrigan of Decatur. "Teachers, nurses, emergency responders and other workers and retirees will not stand by while politicians try to take away their life savings illegally."

The suit was filed one day before Quinn, who is seeking re-election this year, is expected to highlight the pension changes during his State of the State speech to lawmakers. The governor's office didn't have an immediate response to the legal action.

Like the three other lawsuits, the union-led litigation argues that the changes violate Illinois' 1970 Constitution, which states that pension benefits cannot be diminished.

The new law, which affects pensions for an estimated 621,000 teachers, state workers, lawmakers and university employees, reduces annual cost-of-living increases for retirees and raises the retirement age for workers age 45 and younger.

Under the changes, the cost-of-living adjustments would be reduced from a 3 percent compounded increase each year, to a 3 percent, non-compounding boost based on a formula that includes an employee's length of service.

In exchange for a reduction in the cost-of-living adjustments, the new law reduces the amount of money workers are required to pay toward their pensions.

Supporters say the changes will eliminate the state's $100 billion pension debt over 30 years.

Carrigan said offering the reduced pension contribution to employees does not outweigh the other changes.

"The Legislature and governor shirked their responsibility to uphold the Constitution, so we are seeking justice in court to right their wrongs," Carrigan said. "Promises must be kept, and the rule of law must prevail over politics."

The suit was filed on behalf of 25 plaintiffs, including Edward Corrigan of Pontiac, who retired after approximately 20 years as a correctional officer; Marlene Koerner of Herrin, a retired social studies teacher who taught for more than 30 years; and Julie Young of Owaneco, an 11-year employee of the Secretary of State's office.

The lawsuit calculates that Koerner, for example, would lose an estimated $6,595 by the time she turns 85 as a result of the changes.

The suit notes that Corrigan, who receives a pension of about $20,400 per year, will lose about $2,967 by the time he turns 85.

Young, who is not planning to retire until 2030, would see the largest financial impact. Over the course of 25 years of retirement, the lawsuit projects she will see $146,000 less in benefits under the new law.

The 55-page suit notes the plaintiffs have "faithfully" contributed to their pension systems during their tenure with the state.

"Unfortunately, the same cannot be said of the state," the lawsuit states. "The state chose to forgo funding its pension systems in amounts the state now claims were needed to fully meet the state's annuity obligations. Now, the State expects the members of those systems to carry on their backs the burden of curing the state's longstanding misconduct."

Along with the AFL-CIO, other unions involved in the coalition include the Teamsters, the Laborers and the American Federation of State, County and Municipal Employees Council 31, which is the state's largest union.