At work, actor's union reveals unfairness (8)
I believe the answer is:
inequity
'unfairness' is the definition.
(I know that unfairness can be written as inequity)
'at work actor's union' is the wordplay.
'at work' becomes 'in' (eg being in as opposed to being off sick).
'actor's union' becomes 'Equity' (Equity is the trade union for UK actors).
'in'+'equity'='INEQUITY'
'reveals' acts as a link.
(Other definitions for inequity that I've seen before include "Unjust treatment" , "not fair" , "Unfairness, injustice" , "Lack of fairness" , "Prejudice" .)