The Association of Consulting Actuaries (ACA) quizzed 309 firms about the future of their pension schemes. Some 41% of companies with fewer than 250 staff were considering swapping their own schemes with new Personal Accounts that could be less generous.
From 2012, workers will be enrolled in a pension unless they opt out. Consultation on the plans was launched by the government on Thursday.
Under the proposals, if a company pension is not available, workers can be automatically enrolled in the government-backed Personal Accounts. Under this scheme, an employee puts in a minimum of about 4% of their salary into the scheme, Their employer will eventually contribute a minimum of 3%.
"While we support the government's ambition to encourage wider pension coverage through auto-enrolment and Personal Accounts, the survey highlights the complete absence of a coherent plan to support existing quality schemes," said Keith Barton, chairman of the ACA.
"The message is clear - good schemes are falling under threat from these well-intentioned reforms."
The number of employees who are members of a firm's pension scheme is expected to increase when auto-enrolment starts, creating extra costs for employers who contribute to these schemes.
More than half of employers in small firms who were asked said they would revise their pension benefits to offset the increased cost of automatically enrolling staff into an existing scheme in 2012.