Amnesty International has begun an internet campaign to persuade senior British judicial figures not to work with the planned inquiry into the Pat Finucane murder.
The inquiry is to be set up under new legislation that will grant the British government new controls over what is heard in public.
Amnesty's UK director Kate Allen said: "The [ British] government will be able to control what the public finds out, and what it doesn't."
She joined a chorus of criticism of the new legal framework for the proposed inquiry.
The Finucane family and Mr Justice Peter Cory, the retired Canadian supreme court judge who recommended holding an inquiry, have all rejected its terms.
They believe the new measures would hinder the inquiry's independence, effectiveness and openness.
Judge Cory also called for inquiries into other contentious murders in which collusion between security forces and paramilitaries is alleged.
However, these inquiries are to be held under existing legislation which is not contested by the families or human rights observers.
Preliminary hearings have already been held in advance of full investigations into the loyalist killings of human rights lawyer Rosemary Nelson and Catholic Robert Hamill.
The British government has also given the go-ahead for another inquiry into the murder of loyalist paramilitary leader Billy Wright.
A date is likely to be set later this year for the start of that inquiry.
Geraldine Finucane, the murdered solicitor's widow, has already written to senior British judges calling on them not to work with any inquiry operating under the new legal framework.
Her son, Michael, told The Irish Times he welcomed the Amnesty International campaign.
"I appreciate the fact they are raising awareness and putting this campaign on a strong footing," he said.
Claiming that the new Inquiries Act, 2005, would not lead to a sufficiently independent inquiry, Mr Finucane said:
"One of the things that the European Court has determined is there should be a right-to-life inquiry in this case.
"There has been a violation of rights and there should be an investigation which is independent. But how can it be independent under the new Inquiries Act?"
He said his mother had received replies from senior British legal figures.
"The principal reply was sent by the Lord Chief Justice of England and Wales, Lord Woolf," Mr Finucane said.
"He wrote to say he was replying on behalf of his colleagues but added that some may choose to write individually, which they did.
"In his letter he underlined his independence from government and that of all judges. On that basis he said he could not give my mother the assurance she wanted.
"But, significantly, he added that neither could he give the British government an assurance that he would accept a position on any inquiry held under the auspices of the new Act."
Mr Finucane said his family and human rights observers viewed the Inquiries Act, 2005, as "neither Weston Park-compliant nor Cory-compliant".