This paper introduces a new mediation mechanism into agent negotiations. The negotiation mechanism takes a supply-chain perspective to the construction of software services, attempting to co-optimise individual negotiations between services providers and service consumers along the chain. Parties negotiate acceptable ranges of values for either independent or multi-linked issues. This enables mediator agents to collect negotiation information throughout a supply chain and formulate it as sets of optimisation objectives and constraints. Two examples are presented to demonstrate how the model operates.