The government risks undermining confidence in auto-enrolment through "endless changes and delays", warns the National Association of Pension Funds.
Responding to a Department for Work and Pensions consultation on the revised timetable for implementing auto-enrolment, the trade body said it was essential there were no more changes.
The new schedule, published in January, pushed back the staging dates for small and medium-sized employers and delayed an increase in the minimum employer contributions by a year.
The NAPF said delaying staging and phasing dates benefited the Exchequer significantly, because cutting pension saving cut the amount of tax relief that ordinary workers received.
But the response continued: "We believe it is false economy to keep delaying auto-enrolment to temporarily increase tax revenues, as this only adds to future government costs when people retire without adequate pensions."
It acknowledged the extra time given to small and medium-sized companies to implement the legislation would be welcomed by businesses.
It added, however, that schemes and the pension industry now needed to get on with preparing for automatic enrolment with certainty about the rules and timescales.
The consultation closes on Friday.
23% fall since Q1
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More dates to be announced
Lowest level since 2016