The stalwarts of the US buyout industry are facing a class action lawsuit from shareholders in recent take-private deals, a month after the US Department of Justice began to probe private equity firms over anti-competitive practices.

The claimants allege violations in antitrust laws in a number of public-to-private transactions since the beginning of 2003. The suit claims various private equity firms conspired not to outbid one another by sharing information about their bids and agreeing a price in order "for the bidding group to acquire the target for the lowest possible price".