Black Sabbath drummer Bill Ward has said he will not participate in the British heavy metal band's reunion recordings and tour unless he is offered a "signable" contract.
The statement on his website casts further doubt on the much-hyped return of the veteran rockers, who announced last November that the original line-up were getting back together to write and record their first album in more than 30 years.
They also unveiled plans for a world tour in 2012.
But last month, guitarist Tony Iommi was diagnosed with the early stages of lymphoma and, to accommodate his treatment, the band moved from the United States to Birmingham in Britain to continue writing and recording.
The founding members of the heavy metal pioneers were Ozzy Osbourne on vocals, Iommi, Geezer Butler on bass guitar and Ward.
"At this time, I would love nothing more than to be able to proceed with the Black Sabbath album and tour," Ward said on his website.
"However, I am unable to continue unless a 'signable' contract is drawn up; a contract that reflects some dignity and respect toward me as an original member of the band."
He said he worked with the other Black Sabbath members "in good faith" last year and agreed to appear alongside them at the November press conference in Los Angeles.
"Several days ago, after nearly a year of trying to negotiate, another 'unsignable' contract was handed to me."
He said he was keen to play on the new album and tour, and was already packed and ready to leave the United States for Britain to join the band.
Ward described feeling "lousy and lonely," but added that he stood to lose his "rights, dignity and respectability as a rock musician" if he signed the contract offered to him.
"If I'm replaced, I have to face you, the beloved Sabbath fans. I hope you will not hold me responsible for the failure of an original Black Sabbath lineup as promoted."
He also said his motives were not "greed-driven" and that he was not holding out for a big pay day "like some kind of blackmail deal."
Black Sabbath have sold an estimated 70 million records worldwide, and, like other veteran acts with a large fan base, a reunion tour and recording could prove highly lucrative.
The quartet released their last studio album of all original material in 1978 with "Never Say Die."
Osbourne was fired from the band in 1979, leading to changing line-ups for several years. The original foursome reunited for a 1998 release and played sporadically together in the early 2000s.