The Parents for Justice group has said it is unhappy with the prospect of an independent expert continuing the work of the Dunne Inquiry.
The Tánaiste and Minister for Health, Ms Harney, confirmed in the Dáil today that the inquiry into post-mortem practices in Irish hospitals will end at the end of March.
An independent expert is to be commissioned by the Department after that date if the much-anticipated report on the inquiry findings has not been published.
The Parents for Justice group was set up in 1999 by four mothers who discovered their deceased children's organs had been retained without their consent.
Speaking to ireland.comthis afternoon, spokeswoman Ms Fionnuala O'Reilly said she didn't believe the report is nearing completion and believes the Department's decision to end the inquiry will mean further delays in getting to the truth.
"We believe the appointment of an independent expert is substituting one ineffective inquiry format with another", said Ms O'Reilly.
"Obviously we'd difficulties with the inquiry from the beginning given its lack of powers to compel witnesses to attend. We withdrew support for it in 2002 because if its failure to produce any kind of substantive report which we suspect was due to its lack of powers.
"We anticipate that should an independent expert go on to make findings, that these will be subject to legal challenge by one or other of the parties to the Dunne Inquiry, as they will maintain that they co-operated with the inquiry and now they're working with another, and that any findings made against them may well be contentious," Ms O'Reilly said.
"I don't think this proposed expert will enjoy indemnity in terms of his or her ability of naming hospitals, health professionals and health boards who were aware of practices, money transactions and who benefited from financial arrangements.
"Has anybody ascertained the legal status of the documents obtained by the Dunne Inquiry? . . . Even if these documents were transferred to an independent expert, it'll take over 18 months to sift through them all and evaluate all the evidence - it's believed there are over 100,000 documents," she said.
The State has paid out nearly €20 million on the inquiry into the retention of human organs in hospitals. However, a substantive report on the findings has not yet been produced and may not be forthcoming before the deadline of the end of March.