Voluntary participation is a well-established tenet of collaborative public management. Engagement by choice ensures commitment and good faith participation. However, mandating participation in a collaborative process has become necessary in situations involving wicked problems where there is an imperative for cross-jurisdictional and organizational interaction yet no incentive or opportunity for collaboration exists. The CALFED collaborative illustrates multiple ways in which qualities associated with voluntary engagement were instilled in a process in which participation was mandated. A sense of issue urgency, acknowledgement of interdependence between parties, recognition of collaboration as the preferred approach to decision-making, and procedural fairness were fostered through both enabling and constraining strategies exercised by the process conveners. Defection from the process was strategically precluded. Significant process challenges that appear unique to situations in which participation is mandated include sustaining the mandate and managing enduring home agency resistance.