Rules drawn up by the Personal Investment Authority, the industry's watchdog, mean that companies do not have to tell their clients about the extra cost of any additional contributions they make.
About 7.5 million savers with personal pensions and millions of other policyholders are affected. They are almost certain to be asked to increase payments into their existing schemes in the next few years.
Stephen Locke, director of policy at the Consumers Association, said yesterday: "It is pretty disgraceful. It is time that insurers start obeying not just the letter but the spirit of the new regime.
"They should come clean about how much their sales staff are getting so that customers are not in doubt about what is going on."
The new disclosure requirements, introduced in January after a long and bitter battle with the life insurance industry, force sales staff to disclose at the point of sale how much they will earn from a policy they recommend.
Companies also have to give details of any additional setting-up charges they levy on a product, together with projections of what this means for people who have to surrender their policies early.
Intensive lobbying by insurance companies, banks and building societies has led to the PIA agreeing to impose the new rules only on policies sold after 1 January this year. All existing policies are unaffected.
Companies have argued that their computer systems are not able to provide details relating to policies that may have been sold up to 20 years ago.
Millions of endowments sold in conjunction with home loans will not be covered under the new regime. Borrowers who have taken out endowments may well be asked to increase payments to help to pay off their mortgages.
A PIA spokesman said: "The disclosure requirements we have set cannot be retrospective. If an adviser has already sold a product appropriate to a client there is no reason why details of that old policy must be given."