But United are insisting that they have the option to keep the young Frenchman on for another season.
A specially convened Premier League tribunal will sit on Wednesday to rule on the matter.
"As far as we are concerned, West Ham have welched on an agreement that they would not sign Bernard," Shepherd told the Evening Chronicle.
"That's why we dropped our complaint to the Premiership after West Ham tapped him back in March.
"The Premier League accepted Bernard's contract of two years with another 12 months option when we signed him, so why can't they accept it now? Indeed, when is a contract not a contract?
"Our operations director Russell Cushing has been in football for 30 years and he does not make any slip-ups on contracts.
"We have been in the Premiership since 1994 and up to now we have not fallen out with any other club.
"Whatever you may say about Newcastle United we have always kept our word, which is something West Ham have not done.
"What West Ham have done is disgraceful and I will go down to the tribunal on Wednesday and fight this to the bitter end."
West Ham manager Glenn Roeder has confirmed that Sir Bobby has spoekn to him over the left-back, but insists his club have done nothing wrong.