In yet another blow to the bankruptcy-filed Nortel Networks Corp., the U.S. Internal Revenue Services has pressed a claim to $3 billion for back taxes, interest and other penalties, stated a claim filed in the company’s bankruptcy case.

The claim, which was filed on August 20, relates to the period between 1998 and 2008, and lists taxes due of $2.97 billion and interest due of $ 49.3 million.

“We have significant tax loss carry-forwards in the U.S., the size of which have been subject to review by the IRS, however, we are not aware of anything that would lead to a tax liability of that magnitude,” Nortel spokesman Jay Barta said.

Nortel, once the largest North American telecommunications equipment manufacturer, applied for bankruptcy protection in January, following economic crisis rocked the company’s turnaround effort that began in 2005.

Tax claims are often filed against bankrupt companies, but they are by and large reviewed and negotiated between both parties.