Headgear prohibition after trade union resistance (6)
I believe the answer is:
turban
'headgear' is the definition.
(I know that turban is a type of headgear)
'prohibition after trade union resistance' is the wordplay.
'prohibition' becomes 'ban' (synonyms).
'after' is a charade indicator (letters next to each other).
'trade union' becomes 'TU' (abbreviation for trade union).
'resistance' becomes 'r' (electronics abbreviation).
'tu'+'r'='tur'
'ban' put after 'tur' is 'TURBAN'.
(Other definitions for turban that I've seen before include "Headdress worn by Sikh men" , "Nut bar (anag.)" , "But ran out for the headdress" , "Sikh headdress of scarf wound around head" , "Cloth worn as headdress by Sikh" .)