With more than $1 billion in ticket sales, the Broadway musical "Jersey Boys" has spawned many recent attempts to transform pop music to the stage.

But here's a good legal question: Can former cast members publicly perform covers of the original pop music that inspired the show? Or is that tantamount to creating a competing, unauthorized musical? We'll soon have an answer.

In April, Frankie Valli sued former original cast members of "Jersey Boys" for stealing songs, stage elements and copyrighted logos in the creation of their own musical tour. Valli asked a court to issue an injunction preventing further touring by the ex-cast members.

Now comes the countersuit, which alleges that Valli's claims are "motivated by petty vindictiveness and malice" and that he is "using bully tactics better suited for the schoolyard."

The original cast members -- Christian Hoff, Michael Longoria, Daniel Reichard and J. Robert Spencer -- claim they are entitled to continue participating in "The Boys in Concert," a traveling road show where the group performs hits from Valli and the Four Seasons, among other songs.

"These four incredibly talented men have earned the legal right, through years of toil and artistic effort, to tell audiences of the historically accurate fact that they were stars in 'Jersey Boys'," says the group's attorney, Howard Weller. "They sing songs from the 1960s that include some Four Seasons hits, and that doesn't duplicate 'Jersey Boys' any more than John Coltrane's rendition of 'My Favorite Things' copied 'The Sound of Music.'"

In the counterclaim, the ex-cast members allege that the Valli side has threatened the musicians working with them and interfered with relationships with concert venues and promoters. On grounds of tortuous interference, they are claiming at least $1 million in damages.

We'll have to wait and see whether the Coltrane analogy holds up in court. Singing a cover version of a song has never been as legally complicated as this.