Occupational pension scheme members have attacked the switch in indexing benefits to CPI inflation as a Treasury cost-saving exercise aimed at benefitting business over pensioners.
The Occupational Pensioners' Alliance (OPA), which represents two million occupational scheme members, accused the government of rushing through the changes, saying it had failed to consult on the switch from the RPI properly.
OPA members will lobby parliament on Tuesday with a host of other public sector and civil service pension scheme members to try to convince MPs to contest the switch.
OPA executive officer Roger Turner says: "People believe they have a right to the RPI. Morally, they are probably right.
"The government accepted the RPI did not work for the state pension and devalued it, introduced the triple lock and therefore the earnings link to keep its value but they are prepared to devalue everything else by switching to a lower indexation.
"That appears perverse, and it is purely and simply Treasury driven to save money."
OPA said it was seeking legal opinion on the change to see if any conflicts of interest could arise with sponsoring employer trustees.
Trust law says trustees have to look after the interests of beneficiaries and a switch to RPI may violate this principle if it clearly benefits sponsors.
The government is currently consulting on how occupational pension schemes could be affected by the switch to CPI.
Parliament approved a switch for social security benefits last week.
However, Turner says the government has failed to give enough time to such a massive change.
"It has been handled appallingly. It has been rushed in from June and it was not even in a manifesto.
"It has been done far too hastily with pressure from the Treasury with not enough time to consider the consequences."
Our weekly heads-up for advisers
'Nothing can prevent scammers developing workarounds'
Stalwart Scottish Mortgage takes third place
Consistency and compliance vs. slower reaction time
Search for replacement to begin imminently