Robert Plant, left, and Jimmy Page of Led Zeppelin in concert in Chicago, Illinois. in 1977. (Photo by Jim Summaria via Wikipedia.)

The Ninth Circuit is set to hear en banc arguments Monday on a case that could set broad new law on the copyrightability of musical works.

Seventies super group Led Zeppelin and its music labels will square off before the en banc court with the estate of a musician that claims the band copied his song. They'll hash out whether the selection and arrangement of a limited number of musical notes can be copyrighted, and, if so, how much protection such a composition is due. The U.S. government is also chiming in, cautioning the court against "granting a monopoly on a common musical convention."

They're also looking for a definitive ruling on whether sheet music deposited with the Copyright Office or the actual recordings of songs define the scope of copyright protection for pre-1978 musical works. A lawyer for the estate of musician Randy Wolfe says that if he can play Wolfe's 1967 song "Taurus" for a jury, his case against Led Zeppelin would be a slam dunk.

The estate has already lost one minor skirmish before the en banc panel. The court on Tuesday turned down attorney Francis Malofiy's request to play portions of " Taurus" and "Stairway to Heaven" for the judges at Monday's argument on his cellphone. He told the court it would prove that "the two songs are, in fact, virtually identical."

Jurors found in 2016 that the two songs are not substantially similar, but a Ninth Circuit panel last year ordered a new trial. U.S. District Judge R. Gary Klausner had instructed jurors that "common musical elements, such as descending chromatic scales, arpeggios or short sequences of three notes" are not protected by copyright. They should have been told that even a limited number of notes can be copyrighted if selected and arranged in an original way, the panel held.

The panel also backed Klausner's decision not to play a recording of "Taurus" for the jury, on the ground that it's the sheet music deposited with the Copyright Office that defines the scope of copyright under the 1909 Copyright Act. (That law has since been superseded by the Copyright Act of 1976.)

The Department of Justice and Copyright Office weighed in on the case last month, arguing that the selection and arrangement of unprotectable musical elements should be entitled to only "thin" copyright protection. That means only "virtually identical" copying would infringe. Skidmore v. Led Zeppelin can't meet that standard because the notes and the rhythm of the two songs "are not all, or even mostly, the same," the government says. Daniel Tenny of the DOJ Civil Division's appellate staff will present amicus argument for the government Monday.

The government's position led to another round of briefing from the parties in the run-up to the argument. Malofiy, of Pennsylvania's Francis Malofiy Esquire, wrote that "the Trump Administration's" amicus brief is "an embarrassment that fails to understand the applicable law or the history of copyright."

He accuses the government of taking up the music industry's "cause du jour" with the thin-protection argument. Thin copyright might apply to "functional, fact-driven" works. But "artistic works with endless variations, such as songs, by their nature are afforded broad protection, not 'thin' copyright," Malofiy argues.

Representing Led Zeppelin and the music labels, Davis Wright Tremaine partner Peter Anderson argues that the estate didn't make a selection-and-arrangement argument at trial. But if the en banc court endorses that theory for musical works, it must emphasize that the unprotected elements have to be "sufficiently numerous," combined in a sufficiently original way, and be virtually identical in order to infringe, he says.

He wants the court to disclaim language from recent decisions, such as a 2018 case involving Pharrell Williams and Robin Thicke's "Blurred Lines," that he says makes it too easy for plaintiffs to "cherry-pick" snippets of allegedly infringing works.

Chief Judge Sidney Thomas will hear argument Monday along with Judges Susan Graber, M. Margaret McKeown, William Fletcher, Carlos Bea, Sandra Ikuta, Mary Murguia, Jacqueline Nguyen, Paul Watford, Andrew Hurwitz and Bridget Bade.