The US Justice Department has urged state authorities to reject Google's anti-trust claim against Microsoft.
Google complained to regulators that Microsoft's Vista operating system discouraged use of Google search.
Thomas O Barnett, assistant attorney general, sent a memo to state attorney generals encouraging them to drop the enquiry, according to Sunday's New York Times.
Such an action is very unusual and may have had the opposite effect - several states will pursue the case with or without federal help, the paper claims. Before joining the department Barnett was a senior partner in the anti-trust division of lawyers Covington and Burling, which represents Microsoft.
The complaint has not been made public but alleges that Vista slows down Google's desktop search product. It has been made to Judge Colleen Kollar-Kotelly who oversees the Microsoft consent decree - the body set up to police Microsoft's anti-trust settlement with US states in 2001.
More is likely to be learnt at a hearing in front of Judge Kollar-Kotelly later this month.
There's more from the NYT here. ®