Large US companies were audited less frequently by the Internal Revenue Service last year and examinations were less thorough, according to a report to be released on Monday.

The rate of audits for companies with more than $250m (€158m, £127m) in assets fell from 34 per cent in 2006 to 26 per cent last year, its lowest level in two decades, said Transactional Records Access Clearinghouse, a research group at Syracuse University that analyses government data.