Nortel has fallen out with Genband over the purchase price of its carrier VoIP and applications solutions (CVAS) unit, according to Reuters.
The $182m deal, originally announced late last year, was finalised in February, as reported by MicroScope.
But it has now claimed that Genband is trying to "drastically and improperly" reduce the purchase price to $142m.
"This is a disagreement about the clear terms of the sale agreement and, in particular, Genband's attempt to disregard those clear terms," Nortel said.
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According to reports, Genband is seeking to have the US Bankruptcy Court in Delaware take the matter to arbitration.
Genband initially offered close to $300m for the CVAS unit in a stalking horse deal that would have resulted in an auction, but since no other bidders came forward the unit fell to it by default.
Nortel still owes billions of dollars to its creditors and has always maintained its commitment to maximising the value of the various business units it has sold since its bankruptcy, nearly two years ago.