The Law Society has failed to properly investigate miners' complaints against solicitors taking fees from their compensation, according to a report.
1,000 miners have made complaints over the fees issue
Law firms made claims for Vibration White Finger or Obstructive Pulmonary Disease on behalf of miners from a government funded compensation scheme.
But a Legal Services Ombudsman's report questioned whether some solicitors had acted in their clients' best interests.
The Law Society said criticism of their handling of complaints was misplaced.
Under a government scheme, miners with industrial illnesses are compensated, and have their legal fees paid.
But the Ombudsman, Zahida Manzoor CBE, said she found the Law Society had not investigated whether miners were being advised adequately about the costs by their solicitors.
"In the complaints I have investigated I have questioned why miners were asked by their solicitors to make payments to a claims handling-agents when the government would have covered all such costs," she said.
"I am equally concerned that I found in some cases that the Law Society's investigation was inadequate.
"And I am not satisfied that the Law Society could conclude that the service provided by the solicitors was satisfactory or that there was no misconduct on the part of the solicitor.
"I have returned these cases to the Law Society and recommended that the Law Society re-investigates them quickly."
The Law Society has previously advised solicitors to repay any money to miners that was wrongly deducted from their compensation payments.
Shamit Saggar of the society's consumer complaints board described criticism of the way they have handled the complaints as "particularly misplaced".
He said that of the 1,000 complaints received, 700 had been completed and only 12 had been referred to the ombudsman.
"We have told solicitors to make repayments and we are advertising in mining areas to ensure miners know how to find help," he said.
Meanwhile, 45 solicitors have been referred to the Solicitors Disciplinary Tribunal facing allegations of misconduct in relation to the miners' compensation scheme.
The Law Society said it had been the largest series of investigations it had ever undertaken into a single issue.