Classic rock troupe Led Zeppelin's music is once again under the microscope amid allegations its iconic tune Stairway to Heaven draws from a song by an early contemporary: the Los Angeles band Spirit.

Family members of late Spirit guitarist Randy California and a surviving band member said they're seeking a copyright infringement case against the classic rockers.

The allegations, brought by Spirit bassist Mark Andes and California's estate, were raised in an in-depth feature report published in Bloomberg Businessweek last week.

The case comes to light just ahead of Led Zeppelin's planned reissue of its remastered albums, the first batch of which is slated to roll out June 3.

It's alleged the opening measures of Led Zeppelin's smash 1971 hit Stairway to Heaven was derived from Spirit's 1968 song Taurus, an instrumental tune California composed for his band's self-titled debut album.

Spirit crossed paths with or played the same events as Led Zeppelin in 1968 and 1969.

In an interview with the audiophile magazine Listener that was published after his death in early 1997, California had also pointed out the similarities in the two songs.

"The guys made millions of bucks on [Stairway to Heaven] and never said 'Thank you,' never said, 'Can we pay you some money for it?'" he told the magazine.

"It's kind of a sore point with me. Maybe someday their conscience will make them do something about it."

Seeking writing credit

California, his estate and bandmate said there was never a previous legal challenge against Led Zeppelin over Stairway to Heaven due to lack of funds. Now, they are seeking recognition for the late musician via a writing credit on Stairway to Heaven.

It's not the first time musicians, their estates or other representatives have challenged Led Zeppelin over its well-known music, including hits such as Whole Lotta Love and Babe I'm Gonna Leave You.

Over the years, artists such as folk singer Anne Bredon and representatives for influential Chicago blues artists Chester (Howlin' Wolf) Burnett and Willie Dixon have settled copyright infringement suits with the band, which subsequently altered writing credits and redirected relevant royalties.