Industry experts are "horrified" that the Liberal Democrats are considering cutting tax relief on ISAs and pension contributions for the wealthy.
As the party gears up for its annual conference, activists are looking for ways to support the party's principles of fair and rigorous taxation.
Liberal Democrat spokesman Henk van Klaveren confirmed a general consultative session on taxation is planned for party members at this month's conference, and that cutting tax-free ISAs and tax relief on pension contributions for the wealthy have been mooted for possible discussion.
Pension contributions up to £50,000 per year or £1.5m for life qualify for tax relief at individual's marginal rates. Individuals can also save up to £11,280 per year into ISAs.
The potential proposals have been criticised by pension industry figures.
Hargreaves Lansdown head of pensions research Tom McPhail said he was "horrified" at the suggestion, saying the move would undermine confidence in the savings system.
He said: "The idea of capping tax relief for the wealthy was shown to be bureaucratic and unworkable following Labour's attempts on this in 2009. It will do more harm than good.
"Over-riding any policy initiative should be two important questions: will this proposal make the system simpler? Will it encourage engagement in long-termsaving? These Lib Dem proposals would achieve neither of those things."
Saga Group director-general Ros Altman said that while tax relief on pension contributions was a delicate and complex matter that would require in-depth discussion, removing tax-free ISAs would send the signal that the government does not want people to save.
She said: "It would be an absolute disaster for the savings culture in this country.
"Many people rely on savings outside pensions to support them in later life. Savings have already been hit substantially by monetary policy.
"The government needs to extend the tax-free ISA allowance, not get rid of it. By targeting the so-called well off, you disincentivise everyone else."
Van Klaveren stressed that any discussion relating to ISAs, pension contributions and other taxation measures would be "non-binding" and "at the earliest stage of policy development within the party".
He added: "Any proposals would go through several steps of consultation before being adopted.
"Steve Webb is working hard on getting more people saving more effectively for their private pensions, which the party fully supports."
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