A union represented employee is entitled to a union representation during an investigatory interview.

An investigatory interview is one in which management questions an employee about actions that may lead to discipline or an employee reasonably believes that such questions could lead to discipline. 

When a manager gives instruction or general information to an employee, this is not an investigatory interview and therefore the employee does not have a right to union representation under Weingarten.  Similarly, if a manager is merely informing an employee about a discipline decision that has already been made, the employee does not have a right to union representation under Weingarten but may have a right to union representation under the Collective Bargaining Agreement.

Please keep in mind that if a meeting between an employee and a manager starts out as a routine discussion, but then becomes an investigatory interview in which an employee reasonably believes that such questions could lead to discipline, the employee then becomes entitled to union representation.