The family of the Oscar-winning American soul singer Isaac Hayes, who died of a stroke earlier this month, is preparing to take legal action to regain the lucrative rights to many of his hit songs.

Hayes was one of the most successful artists of the 1970s with hits, including the theme from Shaft, Soulsville and Do Your Thing, that earned him a gold-plated Cadillac and a sprawling estate in Memphis, Tennessee.

But the flamboyant entertainer, who was buried last week at a funeral attended by Tom Cruise, Denzel Washington and Wesley Snipes, lost the rights to many of his most successful songs after going bankrupt in 1976.

“A federal court ordered his writer's share rights sold for about $30,000 (£15,000), and they have since earned millions for other people,” said Lance Freed, president of Rondor Music, in Los Angeles, which owns the publishing rights.

“He lost millions, and it was morally and ethically wrong to take it from him. He was devastated. Every time we met, he'd ask, ‘How much would I have earned this year?' I'd always tell him, ‘you don't want to know - it will make you too sad'.”

The singer's son, Isaac Hayes III, said: “He definitely was done wrong.” Family members want to ensure that Hayes's widow, Adjouwa, and their two-year-old son are financially secure.

“I'm very passionate about that,” said Mr Hayes, 33. “If that means me trying to get my father's material back, I'm all for it.”

Hayes's long-time lawyer, Allen Arrow, said this week that the singer's family were “going to do whatever they can” to regain the singer's lost rights.

“I can't rule out litigation,” said Mr Arrow, an entertainment lawyer in New York whose past clients have ranged from Liza Minnelli to Pearl Jam. But Mr Arrow claimed that he hopes to secure the music rights - without Hayes's family having to pay for them - “through good faith discussions and negotiations”. He added: “I would hope that we can retrieve a good part of what he lost.”

Hayes, who died aged 65, lost not only the rights to many of his own biggest hits, but also to the successful songs that he wrote for other artists, including Soul Man, Hold On, I'm Comin' and When Something is Wrong with my Baby, all recorded by the 1960s duo Sam & Dave.

There could also be a fortune in previously unknown Hayes recordings, his son said. “My father had a volume of unreleased work that nobody knows about, from the Stax Records days and beyond,” Mr Isaac said. “There was often too much material to release at the time, but it's still great music.

“There are some good songs, and music that can be remixed, used for soundtracks, samples, ringtones, so many things. And he was working on a new album when he died. People will be hearing Isaac Hayes for many years to come.”

The self-taught musician from Covington, Tennessee, rose to become one of the world's most successful soul artists. The advent of disco music in the mid-1970s slowed his record sales, however, and he fell into severe debt to the Union Planters bank.

In a complex financial restructuring deal the bank agreed to collect all of Hayes's income from his record label, Stax Records, and apply it towards his debts. Stax saw its sales slump, however, and as it slid into bankruptcy in 1976, Hayes was also forced to declare bankruptcy owing $9 million. He lost his home, much of his personal property and future royalties.

The song and publishing rights are divided among three companies: Rondor Music Publishing, Concord Record Group, and Bienstock Publishing, which owns the rights to Hayes's writer's share.

Rondor Music is understood to have reached a voluntary settlement with Hayes in recent years to compensate him partially for his lost rights income, but has declined to disclose the figure.

Insiders believe that Hayes's family intend to use the threat of litigation, and will claim that the bankruptcy judge made an unconscionable decision to sell off the singer's rights at an onerously reduced rate, in order to force the current rights holders to relinquish their ownership, or at least to give up a substantial share of future rights earnings to the family.

Industry insiders believe there could be a lucrative after-life in Hayes's recordings - and not only by re-releasing old hits.

“Isaac Hayes, along with James Brown, remains one of the musicians most extensively sampled by today's hip-hop artists,” said the singer's former business manager, Onzie Horne Jr.

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