In multiple-unit combinatorial auctions both bidders and bid takers can benefit from support mechanisms that suggest new bids for the bidders. We present a support tool called Group Support Mechanism, which suggests bundles of bids to several bidders not among the provisional winners. It improves upon the Quantity Support Mechanism we developed earlier. The efficiency of the final allocation is better when the Group Support Mechanism is used instead of the Quantity Support Mechanism, especially in cases when the efficient allocation consists of three or more bids. (C) 2009 Elsevier B.V. All rights reserved.