Prevent a project resource from tracking time on just one task of a project

Is there a way prevent a project resource from tracking time on one project task but allow them to track time on another (same project).

In other words, if a project resource is working several tasks of a project, is there a way to prevent them from tracking time on a particular task?

In other words, if a project resource is working task a, b and c, how can we prevent them from tracking time on task a? Task a, b and c are on one project.