Uncooperative union may cause a financial problem (8,6)
I believe the answer is:
negative equity
'a financial problem' is the definition.
(I've seen this before)
'uncooperative union' is the wordplay.
'uncooperative' becomes 'negative' (I can't justify this - if you can you should believe this answer much more).
'union' becomes 'equity' (I've seen this before).
'negative'+'equity'='NEGATIVE EQUITY'
'may cause' acts as a link.
Can you help me to learn more?
(Other definitions for negative equity that I've seen before include "borrowing greater than assets - with 22d" , "unable to move for this?" , "financial problem" .)