A mechanism for stopping (100) or releasing a regulating or chronograph mechanism wheel (1) in rotation about a main axis (D), including a control organ (210) operable by a user and linked with a stopping lever (2) including a support surface (20) arranged to cooperate with a complementary support surface (11) of the wheel (1), and movable between a working position where any support surface (20) is distant from the complementary support surface (11), and a stopping position where a support surface (20) is bearing thereon. Also, a timepiece (1000) including regulating or chronograph mechanism including such a stopping mechanism (100).