A scheme for sick miners in England and Wales has been exploited by a few unscrupulous solicitors, a report says.
Many former miners suffer from work-related illnesses
The fund was meant to distribute £3.4bn compensation to 760,000 former British Coal workers many who had suffered serious injuries.
But Lord Lofthouse, a Labour peer, says at least two law firms have made £100m from the scheme, while miners have had their pay-outs reduced by legal fees.
His report on compensation is being handed to the prime minister later.
Lord Lofthouse, an ex-miner, will argue that money should be paid back, which he says is rightfully the miners' and that the Law Society failed to properly investigate miners' complaints against solicitors taking the fees.
He told BBC News: "It's immoral, when men have worked down the mine all their life, they're suffering from this dreadful disease, when the government's been generous.
"I've spent a lot of time over this last 30 years, I presented five bills in the House of Commons on this subject. I haven't worked all these years to fill the pockets of greedy solicitors."
The BBC's Stephen Blears said the process of double charging - taking legal fees from the government and then milking individual's compensation payouts - has been common.
Peter Williamson, chair of the Solicitors Regulation Authority, said the profession's reputation had been "seriously damaged" by the row.
He added: "I'm ashamed that solicitors whose costs are being met by the government should do such a thing.
"Solicitors are supposed to put their clients' interests first, and that is a fundamental, professional principle."
Many former miners have suffered from injuries such as chronic lung disease.
Ian Lavery, chairman of the National Union of Mineworkers, said solicitors who had double-charged miners had put future compensation schemes in jeopardy.