The government suggested the change to inflation proofing last month. However, many pensioners have been promised annual rises linked to a different form on inflation, the Retail Prices Index.
Members of an online forum for pensions experts, Mallowstreet, have written to the government, claiming the change has been imposed on the industry and that a full consultation period is required.
However, the Department for Work and Pensions (DWP) has rejected this and said that the benefits of public and private pensions needed to be consistent.
The CPI measure of inflation has generally risen by 0.7% a year less than RPI
"CPI is the most appropriate measure of inflation for state benefits, and it is appropriate to take a consistent approach for private pensions", said a DWP spokesman.
"As the change affects the requirement for statutory minimum increases, schemes may continue to make more generous provision. No consultation was therefore considered to be necessary."
The CPI measure of inflation has generally risen by 0.7% a year less than RPI. In the next five years the gap between the two is likely to be at 1.2% a year, according to data from the recently established Office for Budget Responsibility.
The coalition government intends to use CPI for the uprating of state pensions, state benefits and also for the inflation-related increases built into the big public sector pension schemes. As the government tries to cut the record peacetime deficit the changes will lead to a huge saving in the state's pension costs.
"Pensions linked to CPI will be lower over a period of time - some estimates put the drop as high as 25%", said Dawid Konotey-Ahulu of Mallowstreet.