NEW YORK (Fortune) -- Don Imus, the tousled and acerbic radio host whose racial remarks engendered a media storm that triggered a swift upending of his career, is not going away quietly even if the imbroglio has all but disappeared from the national conversation in the wake of the Virginia Tech massacre.

For Imus, who made a career out of operating in the murky space between sophomoric humor and high-brow political talk, there is the little matter of about $40 million left on his contract with CBS Radio - whose boss Les Moonves fired the shock jock on April 12. CBS' lawyers contend Imus was fired for cause and not owed the rest of the money.

But Imus has hired one of the nation's premiere First Amendment attorneys, and the two sides are gearing up for a legal showdown that could turn on how language in his contract that encouraged the radio host to be irreverent and engage in character attacks is interpreted, according to one person who has read the contract.

The language, according to this source, was part of a five-year contract that went into effect in 2006 and that paid Imus close to $10 million a year. It stipulates that Imus be given a warning before being fired for doing what he made a career out of - making off-color jokes. The source described it as a "dog has one- bite clause." A lawsuit could be filed within a month, this person predicted.

A CBS spokesman declined comment, and Imus, through his attorney, also declined an interview.

Bo Dietl, a private investigator and author who is a long-time Imus confidante and was a regular guest on the show, has been making the rounds of the cable talk shows defending his friend and had this to say to Fortune: "I just heard that there is a contract in place, and that he can't be fired without a warning."

Imus has hired Martin Garbus, a New York-based attorney at the law firm Davis & Gilbert who is widely recognized as one of the country's most able First Amendment lawyers. Time Magazine, for one, has called him "legendary, one of the best trial lawyers in the country." He's successfully represented the comedian Lenny Bruce against criminal charges on First Amendment grounds, and the writer Robert Sam Anson in a lawsuit filed by Walt Disney trying to halt the publication of a book critical of the media giant.

But in Imus' case, his free speech rights are tempered by the fact that he said what he said on the public airwaves - which are subject to Federal Communications Commission regulations about what is appropriate content.

"[Garbus is] a First Amendment lawyer who's argued many important cases," said Washington, D.C.-based attorney Lynne Bernabei, who has often represented plaintiffs in employment disputes. "I'm sure they're trying to make this a First Amendment case. But the airwaves are heavily regulated by the FCC.

"In my mind there is a big difference between someone who is under contract and is under FCC regulations and someone who speaks out in town hall. This is someone in a heavily regulated industry and who used the public airwaves."

Bernabei also said that any contract stipulations that allow for provocative content on Imus' show are probably balanced by "something in the contract about appropriate content."

She said, "I'm sure CBS has something about conduct - that he can't use profanity and has to abide by FCC regulations."

So under this argument, the case could turn on whether Imus' comments - which referred to members of the Rutgers women's basketball team as "nappy-headed hos" - meets the definition of profanity under FCC guidelines. The FCC, on its Web site, defines profanity as "including language so grossly offensive to members of the public who actually hear it as to amount to a nuisance."

In some people's minds, CBS (Charts, Fortune 500) would have a slam dunk in making that case. Then there would be the matter of whether or not Imus ever quietly received warnings for previous offensive racial remarks. And there were several, including once referring to the New York Times African-American sports columnist Bill Rhoden as a "quota hire" and PBS anchor Gwen Ifill, who is black, as a "cleaning lady."

Meanwhile, Imus plans to retreat to his ranch in New Mexico for the summer before deciding whether to make another go of it on the radio. Many have speculated he could wind up in the unregulated world of satellite radio, but Dietl, his close friend, thinks he'll be back on terrestrial radio. "He's going to take off the summer, but I think he'll be back and stronger than ever," he said.