Aegon is calling on the Personal Accounts Delivery Authority to publish the assumptions it is using to calculate charges.
The firm says it is of strong public interest for Pada to publish models showing costs depending on how many people join, how much they invest and how long they invest for.
It wants to know how Pada will manage the finances if fewer people are auto-enrolled than projected. It says it is difficult to see how the Government can avoid acting as the ultimate guarantor.
Head of pension development Rachel Vahey says: “Unknown factors, such as whether opt-out rates will match expectations, could mean initial charging assumptions are over-optimistic.
“If this leads to costs exceeding charges, there are three options which are not necessarily contradictory.
“Charges will rise, taxpayer subsidies will have to be brought in and/or borrowing will have to increase. We must avoid letting the scheme get into financial difficulties.”