Changes to a contentious accounting rule could force trillions of dollars of off-balance-sheet transactions back onto companies' books, but it will be done in a way to avoid unnecessary shocks in the market.

The assurance to companies came from Securities and Exchange Commission chairman Christopher Cox.

'We want to make sure that the discussion of this and the implementation of this is done in such a fashion that the market can absorb it and it does not create any unnecessary shocks,' Cox told a panel at the US Congress.

The Financial Accounting Standards Board is working to eliminate off-balance sheet special purpose entities which came under fire during the credit crunch, since these were forced back onto the companies' books when their trading floors thinned.

The change would mean that current and new entities will have to be brought onto the balance sheet.

Mortgage companies have raised concern about the changes but Cox said the changes were not being rushed.

'It's wrong to say that this is being fast tracked. The likely scenario is that there will be a period for public comment, consideration. In terms of effective date that they are considering in that proposal, we are talking years into the future,' said Cox.

FASB plans to announce the revised rules next month.

Further reading:

Accountants and the crisis: the outlook - ready for the worst

FASB set to change off balance sheet accounting

US raises $5,000bn balance sheet fears