Yahoo boss Jerry Yang is no stranger to personal fights, but his latest opponent, activist investor Carl Icahn, is threatening to hold Yang and the rest of the Yahoo board personally liable for defensive actions they've taken to protect the company from a takeover.

At issue are the details of a severance plan, which has ratcheted up the heat on Yahoo in the midst of Icahn's proxy fight for the company. Icahn and two Detroit pension funds are suing Yahoo over the failed Microsoft talks, and as part of that suit the plaintiffs have alleged that Yahoo unnecessarily inflated the price of the company by instituting an overly generous employee severance plan.

"If they continue with this line, I believe they (the board) may be personally liable," Icahn told Reuters. "They put in a severance plan that is just a complete and total travesty."

According to Icahn, the plan could add as much as $2.4 billion to the eventual price of the company. But Yahoo disputed that figure, putting the estimated cost of the plan -- should the company be sold -- somewhere between $514 million to $845 million. 

As for the lawsuit, the plaintiffs are pushing for a trial before Yahoo's Aug. 1 shareholder meeting, which is expected to resolve the proxy fight.