A possible record $6 billion-plus profit from the Commonwealth Bank of Australia (ASX:CBA) this week will reawaken issues that major banks are giving a boost to their bottom lines at the expense of clients.

CBA faces extra scrutiny from politicians and consumer groups as it releases its annual results on Wednesday, in the middle of a tighter federal election campaign.

Its net interest margins, the money CBA makes in the various parts of its business after deducting all costs, is expected to be the focus of concern although the responses from investors and customers will have varied reasons.

On the other hand, stakeholders will be worried if margins continue to slump as this will hint that CBA is struggling to keep costs under control, especially the price of its own borrowing from international credit markets.

On the other hand, any increase in margins in spite of these rising costs will be regarded as a signal by consumers that the banking sector is making excessive profits through the fees it imposes on a range of products, specifically on mortgages.

Analysts believe the forecast 40 per cent growth in annual net profit from $4.3 billion at the end of June 2009 to $6.2 billion this year will have been realized as a result of lower margins.

The robust profit expansion is likely steered by a reduction in CBA's bad debt charges and the inclusion of a full year's data from BankWest.

CBA's result will be a useful insight into the possible earnings of the other majors Westpac, ANZ and NAB.