The National Association of Pension Funds has written to MPs ahead of a parliamentary debate urging them rethink proposed pension taxation changes.
The trade body warned the changes - put forward in the Budget - would have a negative effect on pension saving.
The NAPF has already given evidence to the House of Lords economic affairs sub-committee to outline its concerns.
These include the proposals break the long-established "EET2 principle" on which UK pensions have been based by withdrawing tax relief on employee contributions and imposing a tax charge on the individual on his employer contributions.
It said: "Having broken this principle, there is a risk that future governments will make the same changes for those on lower incomes."
The NAPF is also concerned the proposals break the tax simplification framework, introduced by the current government in 2006, and which was intended to be a lasting settlement.
"The constant changes to legislation can do nothing but undermine scheme sponsor confidence in the stability of, and government's commitment to, pensions," the NAPF added.
It also said the proposals ignore the fact that higher earners will also tend to pay tax at higher rates when they retire. And people directly affected by these changes are likely to be those making decisions about company remuneration policy.
NAPF chief executive Joanne Segars said: "The Budget changes send out the wrong messages on pension saving. The government must think again about the wider impact of the new measures as the changes are likely to affect more than just top-rate tax payers.
"The government's proposals break a long established principle tax policy in this country and the constant instability in legislation does nothing to help rebuild badly needed confidence in pensions."
The NAPF has also expressed doubts that the Budget measures will raise the £3.1bn in additional tax revenue HM Treasury predict as individuals seek more tax efficient ways to save and companies look to new ways to reward higher paid staff.IFAonline
Clarke replacing Balkham
'Deep-dive analysis of client behaviour'
Ways to mitigate April’s increases
The best equity income funds examined