See Fair Work Act 2009 s.387(a)
The reason must be 'sound, defensible or well founded.' A reason which is 'capricious, fanciful, spiteful or prejudiced' cannot be a valid reason.
'[T]he reason for termination must be defensible or justifiable on an objective analysis of the relevant facts.' It will not be enough for an employer to say that they acted in the belief that the termination was for a valid reason.
The valid reason for termination is not to be judged by a legal entitlement to terminate an employee, 'but [by] the existence of a reason for the exercise of that right' related to the facts of the matter.
The Fair Work Commission does not 'stand in the shoes' of the employer but will need to be satisfied that the termination of the employee was for a valid reason.