Anti-unionism, note, very high (8)
I believe the answer is:
misogamy
'anti-unionism' is the definition.
'note very high' is the wordplay.
'note' becomes 'mi' (as in 'do re mi').
'very' becomes 'so' (I've seen this in other clues).
'high' becomes 'gamy' ('gamy' can be a synonym of 'high'**).
'mi'+'so'+'gamy'='MISOGAMY'
(Other definitions for misogamy that I've seen before include "dislike of unions" , "Hatred of marriage" .)