Led Zeppelin is being sued for allegedly ripping off their most famous song “Stairway to Heaven” from another band’s tune. The now-defunct Spirit has been accusing the English rock band for decades, but has just now decided to lawyer up to make their case official.

As reported by Business Week, Spirit’s founding bassist Mark Andes is beginning a process to ensure that Led Zeppelin would be forced to acknowledge that it has indeed ripped off the chords of “Stairway to Heaven” from Spirit’s 1968 track “Taurus.”

Guitarist Jimmy Page apparently heard a riff from “Taurus” when Led Zeppelin toured with Spirit in 1968. He reworked the riff into the opening notes for “Stairway” when they released the song in 1971.

But instead of crediting Spirit for the song, Page is accused of claiming it as his own.

“Stairway crystallised the essence of the band,” he said to Rolling Stone magazine in 1975. “It was a milestone for us. Every musician wants to do something of lasting quality, something which will hold up for a long time, and I guess we did it with Stairway.”

Randy California (real name Randy Wolfe) was the original writer of the song. He died in 1997, but a trust handling his royalties is teaming up with Andes to sue the legendary rock band.

“Taurus,” which runs for two minutes and 37 seconds, may have a case. According to some listeners, the plucked guitar line about a minute of the song sounds suspiciously similar to the opening sequence of “Stairway.”

“I’d say it was a rip-off,” California told Listener magazine in 1997. “And the guys made millions of bucks on it and never said ‘Thank you,’ never said, ‘Can we pay you some money for it?’ It’s kind of a sore point with me. Maybe someday their conscience will make them do something about it.”

But as it turned out, Spirit has to lawyer up before they even get a chance at making Led Zeppelin admit that its signature song was taken from another band.

This isn’t the first time Led Zeppelin has been accused of plagiarism. The rockers – Page, singer Robert Plant, bassist John Paul Jones and drummer John Bonham – have reached settlements with other musicians over their apparent plagiarism of some of their famous songs, including “The Lemon Song,” Babe I’m gonna Leave You,” “Whole Lotta Love” and “Dazed and Confused.”

Led Zeppelin’s “Stairway to Heaven”

Spirit’s “Taurus”