Last month government lawyers sent similar letters to at least four prominent buyout firms: Carlyle Group, Clayton, Dubilier & Rice, Kohlberg Kravis Robert and Silver Lake Partners. The federal inquiry is said to be in its early stages. It's not clear that at the end of the day the government will be able to prove collusion between private equity firms, which have raised a record amount of money this year for corporate buyouts. The government probe is focusing on so-called "club deals,'' a situation in which several private equity firms get together to buyout a company. Government lawyers are trying to determine if these club deals are a away for private equity firm to control the bidding process for a company by offering rival firms a chance to co-invest in deals. The allegation is that the lack of competition keeps the takeout price for a company relatively low.