In 2013, the General Assembly and Gov. Pat Quinn approved a plan they said would put the state employee retirement systems on a road to recovery.
That plan currently is in front of the Illinois Supreme Court, which is set to hear oral arguments in the case in March.
If the high court rules the law is unconstitutional, Rauner and the General Assembly will be back to square one when it comes to finding potential savings.
Although there are a number of routes they could go in an attempt to control the rising costs of pensions, Rauner is already ruling out one of them: Taxing retirement income.
"I have no plans to tax retirement income," Rauner told reporters during a stop in Springfield last month.
FILE - In this Aug. 15, 2012 file photo Mike Phillips, of Vandalia, Ill., and other union protesters, supporters, and labor leaders boo Illinois Gov. Pat Quinn in protest saying he is betraying the Democratic party's tradition of supporting working men and women, during Governor's Day at the Illinois State Fair in Springfield. The ability of Illinois unions to withstand the pressures that broke down their colleagues in other states could be tested during a veto session beginning Tuesday, Nov. 5, 2013, as lawmakers try for the umpteenth time to confront the nearly $100 billion shortfall in the public-employee pension system, the largest in the nation. The Legislature is under pressure to consider slashing pension benefits or requiring employees to contribute more to their own retirement funds or to retire at a later age. (AP Photo/Seth Perlman, File)