Led Zeppelin was known for borrowing lyrics and melodies from the blues legends they admired, but now the group is being accused of lifting the iconic intro to “Stairway to Heaven” from a forgotten California group that they toured with in the late ‘60s.

It turns out that the opening to the 8-minute track on Led Zeppelin IV sounds very similar to “Taurus,” an instrumental track that appeared on the self-titled debut album from Spirit. That group, which did score a hit single with “I Got a Line on You,” did tour with Led Zeppelin in 1968 and 1969. So, it is possible that Led Zeppelin guitarist Jimmy Page heard the track.

Mark Andes, Spirit’s first bassist, told Businessweek that “Taurus,” written by their guitarist, Randy California, was a fixture of their setlist. He believes that Page and the other members of Led Zeppelin must have heard the track.

Andes believes that the group continued to bring in more and more Spirit music as they continued to perform in the U.S., including incorporating their song “Fresh Garbage” in medleys.

While California himself has been relatively quiet about the possibility that “Stairway” was plagiarized, members of Spirit are now working with attorney Francis Alexander Malofiy. They hope to get the planned reissue of Led Zeppelin IV stopped.

“The idea behind this is to make sure that Randy California is given a writing credit on ‘Stairway to Heaven,’” Malofiy told Businessweek. “It’s been a long time coming.”

This is hardly the first time that anyone has sought writing credit for a Led Zeppelin song. One of their other iconic hits, “Whole Lotta Love,” was accused of including parts of a Willie Dixon song without crediting the legendary bluesman. Decades after the track was released, Dixon finally got a writing credit.

“Within the lyrics of it, there's [Dixons's] ‘You Need Love,’ and there are similarities within the lyrics,” Page admitted to the New York Times this month, notes Rolling Stone. “Now I'm not pointing a finger at anybody, but I'm just saying that's what happened, and Willie Dixon got credit. Fair enough.”

Members of Led Zeppelin did not comment on the Businessweek story.