AIB has already imposed the penalties, docking as much as 3% off encashments from certain Ark Life funds.

Meanwhile, other financial institutions have not ruled out taking similar action, especially around next May, when more than 40% of SSIAs will mature in a single month.

The penalties are imposed when investment funds are swamped by encashments such as maturing SSIAs, so that there is more money going out than coming in. To S pay for the encashments, funds are forced to sell off some of their investments, triggering trading commissions and stamp duties.

According to Frank O'Dwyer, chief executive of the Irish Association of Investment Managers, the penalties ensure that only investors bailing out are hit for these trading costs, and not those people who leave their money in the fund.

"Because of strong underlying inflows, our members are confident that instances of net outflows over the coming months should not be high, " he said.

Gareth McQuillan, marketing director at Hibernian Life & Pensions, which manages the Ark Life funds, said the penalties were likely to be temporary.

"We believe we will be in a position in the future where cash flows will turn positive again, " he said. "The majority of customers who stay invested will not be affected by this temporary change in fund pricing."

The biggest providers of equity-based SSIAs, Irish Life and Bank of Ireland, played down the chances of exit penalties for maturing SSIAs but refused to rule them out.

Both reported strong cash inflows to all their funds, which they said should be enough to accommodate SSIA encashments.

Brendan Johnston, marketing director at Eagle Star, said investors should keep a close eye on how fund managers react.

"We can't say this won't be a problem and it's something people need to look at as their SSIAs come up for maturity, " he said.