'We have observed a new nervousness among US corporates related specifically to the SarBox regime. Deals are taking longer as CFOs take pains to ensure that they can certify the accounts and controls of target businesses,' said Simon Russell, a corporate finance director at Deloitte, who carried out the research.

He added that some companies were completely deterred from certain transactions altogether because of the new rules.

The Securities and Exchange Comission recently introduced an exemption allowing companies carrying out acquisitions in the year of section 404 certification to leave the acquired business out of the scope of testing and assessment. But they have to disclose whether the new business has been excluded from the requirements and the impact of that business upon the consolidated results.

'Some businesses have decided they are not prepared to risk the potentially negative signals sent by excluding recent acquisitions from SarBox, particularly those mega deals that account for a large element of the business,' said Russell.