Defiant trade union's bid curtailed undergoing restructure (13)
I believe the answer is:
Here is my best explanation:
'defiant' is the definition.
('insubordinate' can be similar in meaning to 'defiant')
'trade union's bid curtailed undergoing restructure' is the subsidiary indication.
'curtailed' means to remove the last letter.
'undergoing restructure' indicates an anagram.
'tradeunionsbid' with its last letter removed is 'tradeunionsbi'.
'tradeunionsbi' anagrammed gives 'insubordinate'.
(Other definitions for insubordinate that I've seen before include "Badly behaved", "Insolent", "Cheeky", "Not submissive to authority", "Disobedient", "Recalcitrant", "undisciplined", "Mutinous", "Rebellious" and "challenging authority".)