More than 700 figures from the legal profession have criticised government plans for secret courts as "contrary to the rule of law".
The group has called for the measures to be ditched, warning that the Justice and Security Bill is "dangerous and unnecessary" and will "fatally undermine" the fairness of court hearings.
In a letter to the Daily Mail, leading lawyers, including 38 QCs, claim the closed doors hearings will "erode core principles of our civil justice system".
Among the signatories is Nicholas Vineall QC, a former chairman of the Conservative Lawyers' Association and Ian Macdonald QC, who resigned as a security-cleared special advocate in protest at the existing use of secret justice.
The Rev Nicholas Mercer, a lieutenant colonel who was the Army's most senior lawyer during the Iraq war, also signed the letter. He told the Daily Mail: "The Justice and Security Bill has one principal aim and that is to cover up UK complicity in rendition and torture.
"The Bill is an affront to the open justice on which this country rightly prides itself and, above all, it is an affront to human dignity.
"The fact that some of those individuals who are complicit in rendition and torture can not only assist in the drafting of the Bill but also vote to cover their tracks is a constitutional scandal.
"It is little wonder that the Bill has been heavily criticised by the UN Rapporteur on Torture and condemned by the vast majority of lawyers and human rights organisations in this country."
The legislation, which would allow judges to order a "closed material procedure" (CMP) so that secret evidence can be heard behind closed doors in order to avoid the exposure of information which could harm national security, is expected to return to the Commons next week.
Minister without portfolio Kenneth Clarke, who is in charge of the Bill, told the Daily Mail it was being tweaked further.
He said: "This Bill is now proportionate, sensible and necessary. It resolves the highly unsatisfactory legal no-man's land we have at the moment where national security cases can be brought, but not resolved.
"Of course these amendments will not reassure the Bill's hardline critics, who prefer silence to judicial decisions on allegations of kidnap and torture, and are prepared to accept that millions of pounds could go without challenge to individuals who could be terrorists. These final amendments should now resolve all right-thinking citizens that this is a sensible, worthwhile Bill which they would give their support to."