Rachel Reeves has attacked Steve Webb for "changing the rules of the games" in switching from RPI to CPI.
The government has calculated the move from RPI to CPI indexation for occupational schemes could reduce the value of pension rights by as much as £76.6bn over 15 years.
Steve Webb has said the government will not give private sector schemes the power to override scheme rules to shift from RPI to CPI indexation.
Defined benefit scheme deficits have rocketed by about 50% over the past four years jumping from an average of £55bn to £87bn, figures show.
An industry-wide consultation on the RPI to CPI switch will be issued tomorrow, Steve Webb says.
Proposed changes to public sector pensions are "unpalatable" as previous cuts have already slashed pots by 25%, delegates heard.
The top 100 UK firms' defined benefit schemes knocked £42bn off their combined deficit over the last year, Pension Capital Strategies research shows.
More than 10 million people will see their state second pension hit by the Consumer Price Index switch by the end of this parliament, the government says.
Pension reform is continuing at a relentless pace but can the industry keep up? Helen Morrissey reports
Sebastian Cheek urges the government to make a firm decision on the switch to CPI