Employment-relations scholarship frequently associates organisational sustainability with industrial harmony, cooperation, effective dispute resolution and declining workplace conflict. Such indicators, however, cannot distinguish disagreement that has been institutionally regulated from disagreement that has become less visible because employees lack effective means of contestation. This conceptual paper develops institutional conflict-regulation capacity as a system-level construct for explaining how employment-relations institutions process disagreement under unequal power. Drawing on critical pluralism, structured antagonism, employee voice and institutional regulation, the framework identifies four interacting mechanisms: procedural fairness and reviewability; protected and effective employee voice; independent collective representation and bargaining; and credible institutional enforcement. Power asymmetry operates as a boundary condition rather than a fifth mechanism, while adaptive institutional learning operates recursively through conflict, institutional feedback and redesign. The framework distinguishes three conflict trajectories—regulated, suppressed and escalated—and argues that low visible conflict is not necessarily evidence of sustainable employment relations. Nigerian public, private, multinational, informal, temporary-agency and platform work provide contextual grounding for the framework rather than empirical validation. The paper's contribution lies in integrating established mechanisms into a conditional conflict-regulation architecture and specifying how their interaction changes under unequal power. Keywords: Pluralism, Power, Voice, Bargaining, Enforcement