Suing an opposing lawyer over an effort to settle a case for money is extremely unusual, said Stephen Gillers, vice dean at New York University Law School and an expert on legal ethics. "Telling someone you will seek legal redress unless they are willing to pay a certain cost is not within the extortion statues," Mr. Gillers said, "as long as you have a plausible basis for your legal claims."

He said that suggesting Mr. Morelli had a political motivation [...] was simply not relevant. "It won't work in the courtroom," Mr. Gillers said. "It may play better in the tabloids, but not in a courtroom."

He added, "Fox is being so aggressive it suggests to an outsider that Fox and Mr. O'Reilly are quite worried about this lawsuit."

Plato Cacheris, a former lawyer for Lewinsky, said potential plaintiffs negotiating for money is "very routine: 'I'm thinking of suing you but I'd like to discuss a settlement.'"

Debra Katz, an attorney who specializes in sexual harassment cases, said that when a company sues an employee who is about to file a harassment complaint, "the courts are more inclined to see it as a retaliatory lawsuit." Asked if Mackris's case was weakened by her decision to return to Fox, Katz said O'Reilly's alleged conduct "went from what could be seen as sexual banter about 'you should buy a vibrator' to really disgusting, unwelcome sexual remarks."

But Washington lawyer Lanny Davis said he would have advised O'Reilly to seize the offensive because "when a charge of sexual harassment makes the headlines, you are presumed guilty until proven innocent. That's a reality, whether it's fair or not."

Lisa Bloom, a Court TV anchor and veteran sexual harassment attorney, said Morelli's and Mackris' demand for $60 million, which led Fox to sue for extortion, "is an extraordinarily high number. And in my experience, in a lot of these cases against celebrities, $4 million to $6 million would be high."

But, she added, "It looks like she has a viable claim ... If she's got tapes [with him]* making these extremely explicit comments to her, she's got a strong case, and it would be clearly sexual harassment under New York law. The only defense is that she welcomed, encouraged and participated in it, and I haven't heard Fox say that so far."