Lawyers and the Personal Investments Authority, the financial watchdog, have clashed over the mis-selling of personal pensions in the 1980s.
Disagreement has surfaced because life companies have been told by the PIA that investors pursuing litigation against them need not be included in an industry-wide compensation review.
The review was ordered last year by the chief City watchdog, the Securities and Investments Board.
Philip Ryley, of Ringrose Wharton, whose firm is representing 100 clients pursuing actions, said: "The PIA h
as stated that where an investor chooses to pursue a legal remedy through the courts, the PIA wouldn't require a member firm to continue with a proactive review of the investor's case."
Ryley fears the regulator's stance will put pressure on claimants to drop their cases against investment groups for fear of losing out in the review.
He added: "The purpose of litigation is not to take people out of the review. This development puts pressure on claimants to abandon legal action. It is the equivalent of obtaining a stay on proceedings by the back door."
Ryley said litigation was necessary because the review was taking longer than expected and it may not give everyone full redress.
He denied that there was any question of getting claimants compensation from both the review and through legal claims. Ryley suggested that if review deadlines are met and compensation sums are agreed in advance of hearings, litigation can be dropped.
The latest wrangle came to light when life companies such as the Prudential and Legal & General told Ryley that the PIA's advice was not to pursue reviews in cases where litigation is outstanding.