To solve a multiple criteria decision problem by a collaborative group is necessary to have an adequate coordination process. This paper discusses an on-going research project, which aims to develop an internet-based Multiple Criteria Group Decision Support System (MCGDSS) - which will support to collaborative group decision makers in reaching a consensus when they try to solve a ranking problem - and to further investigate the impacts of such a system on group multiple criteria decision aid (MCDA) process performed in parallel and sequential coordination modes. Features of the MCGDSS prototype and design of a follow-up laboratory experiment are described in this paper.