Legislation passed by Congress that changes how pension plan liabilities are calculated for funding purposes should translate into near-term relief for companies struggling with shortfalls, but won't eradicate long-term shortfalls.

"While the new federal provisions reduce the amount of minimum required pension contributions, we believe such relief only postpones funding improvements and that companies are still on the hook for billions in underlying obligations," according to Fitch Ratings.

The funding stabilization uses interest rates smoothed out over a 25-year period as a starting point for determining discount rates, with rates in 2012 limited to 90 percent of the 25-year average. Changing the discount rate, in the absence of other actions, only changes the present value of the liabilities, as future benefit payments are not changed, the company said.