Most playwrights have jitters on opening night, but David Adjmi was in a panic amid the festivities last month for “3C,” his darkly comic deconstruction of the 1970s sitcom “Three’s Company.” That same day he learned that the copyright owner of “Three’s Company” had sent a cease-and-desist letter to the play’s producers charging that Mr. Adjmi had infringed on the copyright by borrowing so many elements from the TV series, including its premise about a man who pretends to be gay to live with two female roommates.

The show went on — but the copyright fight remains far from resolved.

At issue is whether “3C” is enough of a parody of “Three’s Company” to be protected under First Amendment exceptions to copyright law — specifically, under the legal doctrine of fair use, which allows artists to use copyrighted work to lampoon or critique the material, as the international hit “Forbidden Broadway” has done for years with its sendups of famous musicals.

But another issue is personal, at least in this case: The ability of a financially strapped, largely unknown playwright to fight legal threats.

Fearing the potential legal bills, Mr. Adjmi, 38, said that he initially agreed — in an e-mail sent through his agents — to the demands of the “Three’s Company” owners that he turn down any future productions of “3C” or any publication or circulation of the script, in effect allowing his play to die after its Off Broadway run at Rattlestick Playwrights Theater, which ended on Saturday.