Investors have been spooked by a government plan to impose a new levy on bank deposits, in a move that is forecast to raise $733 million in its first four years and help Labor's pledge to balance the budget.

Big bank shares bucked the trend to fall on Thursday - losing as much as $9 billion of their combined value - as it emerged the government was planning the levy to fund any future bailouts.

The Reserve Bank and the International Monetary Fund support the levy being introduced. Credit:Ian Waldie

From 2016, the year in which Labor has said the budget will be back in the black, it plans to introduce a 0.05 per cent levy on government-guaranteed deposits of less than $250,000.

Money raised would be placed in a government-managed fund - and could only be used to refund depositors, not for other types of spending.