Goldman Sachs Group Inc. (GS) and Bain Capital Partners are set to defend what they call legitimate private-equity practices against investor claims that buyout firms and their bankers colluded to rig bids on takeovers.

The defendants, who also include Blackstone Group (BX)Carlyle Group (CG), KKR & Co. (KKR), Apollo Global Management (APO) and JPMorgan Chase (JPM)g, are scheduled to argue today and tomorrow before U.S. District Judge Edward Harrington in Boston that a proposed antitrust lawsuit by shareholders in the acquired companies should be dismissed