Asymmetric joint action describes scenarios in which a decider oversees goal attainment, while co-actor(s) contribute as followers. When conflict arises, deciders must resolve competing response options (underdetermined responding), whereas followers must prioritize the decider’s information (selection-for-action). To examine this role-dependent conflict management, we introduce a novel online paradigm where conflict is elicited by a co-actor’s competing response. The participant and a co-actor collaboratively move a target via key press from the bottom center to a top corner of the computer screen (relay-like). First, the participant covertly chooses one corner (left/right), then the co-actor overtly moves the target to an intermediate position (left/right), either congruent or incongruent with the participant’s choice. Finally, the participant moves the target to its final position (left/right). Critically, in the basic paradigm, participants first always had to follow the co-actor’s input (follower block); then they were free to follow either their own or the co-actor’s choice (decider block). Across five experiments (leader block, reversed block order, variations in co-actor visibility), we observed that congruency effects were significantly amplified in decider blocks and more so when the co-actor was visible. In addition, congruency sequence effect were present in all experiments. These findings suggest that co-actor-triggered response conflicts are processed differentially depending on freedom of choice, substantiating complementary roles of conflict monitoring (response conflict in deciders) and selection-for-action (information conflict in followers/leaders) in conflict management. Moreover, they extend the scope of cognitive control to free-choice contexts and a novel type of conflict task.