The U.S. government agency that insures worker pensions is worried that a plan by Sears Chairman Eddie Lampert to buy the bankrupt retailer could leave it shouldering more of the company's retirement costs for 90,000 Sears and Kmart employees and retirees.

The Pension Benefit Guaranty Corp. has weighed in against Lampert's $5.2 billion offer for Sears in papers filed in U.S. Bankruptcy Court. The PBGC's legal objections come as the 126-year-old department store chain tries to rid itself of pension plan obligations while under bankruptcy protection, according to debt experts.

The PBGC could be liable for what it says is a $1.4 billion shortfall in Sears' pension plans. While the agency filed claims against Sears in bankruptcy court over that funding gap, it will ultimately have to pay the difference, said Sarah Foss, a legal analyst at Debtwire, a news and data provider.

Get Breaking News Delivered to Your Inbox

More specifically, the PBGC objects to the acquisition offer for Sears by Lampert's hedge fund, ESL Investments, because the agency would lose interests in licensing agreements related to the retailer's Kenmore and DieHard trademarks that the PBGC had previously received. That would result in the PBGC losing royalties, the agency noted in its court filing.

Sears dumping pension costs

The PBGC protects the pension benefits of nearly 37 million Americans in private-sector plans, and currently funds the benefits for about 1.5 million people in failed pension plans, according to the agency. The PBGC get no taxpayer dollars but is instead funded by insurance premiums and recoveries from failed plans.

The agency earlier this month said it was taking steps to assume responsibility for defined benefit pension plans covering about 90,000 Sears and Kmart employees and retirees. The PBGC added that it has for several years worked with Sears to financially shore up its pension plans.

As part of that effort, the agency negotiated a deal with Sears under which the PBGC would take a stake in the company's Kenmore appliance and DieHard battery brands. The agency is now arguing that Lampert acquiring Sears would harm its interests in both brands and the royalty payments that come with them.

"What's unusual here is this complicated transaction where PBGC has a stake in Kenwood and where royalties were flowing to it, this is going to eliminate that stake to them," Foss said.

Only bid in town

Sears filed for bankruptcy protection in October, and the retailer's unsecured creditors have argued that keeping the company around mostly benefits Lampert and ESL.

A committee of unsecured creditors is asking a judge to let it sue Lampert and ESL over Sears' downfall, calling ESL's current bid to save the company "nothing but the final fulfillment of a years-long scheme to deprive Sears and its creditors of assets and its employees of jobs while lining Lampert's and ESL's own pockets."

ESL declined comment. The hedge fund and Lampert have previously defended their plan as a good-faith effort to keep hundreds of stores running and save 45,000 jobs.

"From ESL's perspective, eliminating the pension liability is part of how they make this a viable entity," Philip Emma, a retail analyst at Debtwire, told CBS MoneyWatch.

The fact that Lampert's proposal is the only one that would keep the storied retailer going, at least for a time, likely weighs in his favor.

"It might be hard to imagine the bankruptcy judge saying they are going to eliminate Sears' only option to continue as a going concern," Foss said.

The next court hearing on Lampert's bid is scheduled for Monday.