Federal lawmakers should consider revamping the Pension Benefit Guaranty Corp.'s premium structure so that premiums employers pay the agency more fully reflect the risks their pension plans pose, the Government Accountability Office reported Thursday.

“By adopting a structure that allows rates to better align with the risk posed by individual plans and sponsors, Congress has an opportunity to help PBGC contain its deficit and strengthen PBGC's ability to remain solvent to the future,” the GAO said.

But before revamping its decades-old premium structure, in which employers pay a base premium, plus an additional premium tied to plan underfunding, lawmakers should consider establishing an independent advisory committee, the GAO said.

That committee — comprised of employer, insurer, labor, actuarial and federal agency representatives — would assist with “such activities as developing the mechanics for incorporating additional risk factors and implementation of new rates,” the GAO said.

The GAO report comes nearly two years after the PBGC outlined an approach in which premiums paid by employers would be based at least in part on their credit ratings. At the time, PBGC Director Joshua Gotbaum said that pension plans sponsored by an employer with a top credit rating, for example, doesn't pose the same level of risk as those with a subpar rating.

Employer groups, though, have opposed such an overhaul of the PBGC premium stature. Last year, more than 20 business groups including the American Benefits Council, the ERISA Industry Committee and the U.S. Chamber of Commerce, sent a letter to members of Congress stating such a premium structure would be ill-advised and inappropriate.

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“Leaving aside the question of whether the PBGC can establish accurate mechanisms for measuring and adjusting an employer's credit risk across industries and across the country, even modest year-to-year changes in those government credit ratings could have implications beyond PBGC premiums, potentially affecting stock prices or the company's access to other credit sources,” the groups said.

The GAO report, requested by Senate Health, Education, Labor and Pensions Committee Chairman Tom Harkin, D-Iowa, comes at a time of new challenges facing the PBGC.

A growing number of employers, as part of de-risking approaches, are offering pension plan participants the opportunity to convert their annuities to lump-sum payments. In addition, two big employers — General Motors Co. and more recently Verizon Communications Inc. — have purchased giant group annuities from Prudential Insurance Co. of America in which Prudential will be responsible for paying pension benefits to tens of thousands of their retirees.

Through those actions, PBGC, which in 2011 reported a record $26 billion deficit, will lose millions of dollars in premium income because premiums paid by employers are based partly on the number of participants in their pension plans. That income is used to help pay benefits in failed pension plans the agency has taken over.

Currently, the base premium is $35 per plan participant. However, legislation Congress passed this year will raise the premium to $42 in 2013 and to $49 in 2014.

In addition, the law increases the variable rate premium that is assessed on employers with underfunded plans.