Is being taxed twice possible? It shouldn't be but Brad Twentyman, a director in the superannuation division of the accountancy firm Pitcher Partners, says tighter rules on claiming super tax deductions could result in double taxation for unwary investors starting a pension. In the worst case, they could find themselves slugged with taxes of up to 93 per cent if they don't get all the paperwork correct.

How on earth could that happen? If you're eligible for a tax deduction on your personal super contributions, you have always been required to notify your super fund how much of your contributions will be tax deductible. That way your super fund will know what proportion of your contributions is subject to the 15 per cent contributions tax.

Twentyman says many investors are unaware the notification requirements have been tightened under the new simpler system. He says the first change is the notification must now be made on a Tax Office form. If the notice is not made in the required form, it technically won't meet the eligibility requirements for claiming a tax deduction.

He says the timing of when these notices must be lodged also has changed. Under the old rules most investors notified their funds when they lodged their annual tax returns. That gave them time to get their finances in shape and work out what proportion of the contributions should be tax deductible.

The Tax Commissioner also had the discretion to allow amendments - generally for up to four years.

If you're still in the accumulation phase, Twentyman says, you still have until the date you lodge your tax return to get your form in. But if you're starting a pension - as investors increasingly are doing once they turn 60, regardless of whether they're still working - that may be too late. Under the new rules, Twentyman says investors will be denied a deduction on their contributions if the fund has started to pay a pension based in whole or in part on that contribution.

Let's say you're planning to start a pension on July 1. To maximise your pension, you make the maximum deductible contribution of $100,000 before June 30. But if you don't get your notice in before June 30 (and in the required form), you will be denied the tax deduction on your $100,000. Depending on your marginal tax rate, that could mean an unexpected tax slug of up to 46.5 per cent.

You mentioned taxes of up to 93 per cent. Does it get worse? It can, as contributions on which you are denied a tax deduction will count towards your after-tax or non-concessional contributions limit. If you have already made the maximum non-concessional contribution, your $100,000 will be treated as an excess contribution and taxed at the top marginal rate of 46.5 per cent. The combined effect of this and the foregone tax deduction could result in up to $93,000 tax being paid on that $100,000 contribution.

How can I avoid this problem? If you know how much of your contributions you want to claim a deduction for, you should complete the notice form (ensuring it's the required Tax Office version) at the time you make your contribution. That way your deduction will have been properly accounted for before you start your pension. If you are unsure of your tax deduction, Twentyman says another option is to start your pension as planned but ensure the pension account does not include any of the contribution against which a deduction may be claimed.

That's less efficient as it means your contribution will still be in the accumulation phase where earnings are taxed at 15 per cent and you will probably need to switch the money across to the pension account after the form has been lodged. But it beats losing the tax deduction.

Are there any other wrinkles? The Tax Office is also warning investors about in specie contributions to super funds. In specie contributions involve investors transferring assets to their fund instead of making a cash contribution. In specie contributions are treated in the same way as cash contributions for tax but you must be sure the transfer complies with the super legislation. With new caps now applying to both deductible and after-tax super contributions, Tax Commissioner Michael D'Ascenzo says the fund must make sure it accurately reports the market value of any assets received as in specie contributions.

"We are concerned about contributions ... where the market value of the asset is not properly accounted for in an attempt to avoid paying excess contributions tax," he says.

He says the Tax Office is also on the watch for people trying to avoid the excess contributions tax by paying expenses on behalf of their fund, or by making improvements to a fund asset without reimbursement for the work.