Prohibit the trade union creating languages (5)
I believe the answer is:
bantu
'languages' is the definition.
(I have seen 'African languages' mean 'bantu' so perhaps 'languages' could also mean 'bantu')
'prohibit the trade union' is the wordplay.
'prohibit' becomes 'ban' (banning is a kind of prohibiting).
'the trade union' becomes 'TU' (abbreviation for trade union).
'ban'+'tu'='BANTU'
'creating' acts as a link.
(Other definitions for bantu that I've seen before include "Central and southern African native" , "Group of Niger-Congo languages" , "Group of languages including Swahili and Xhosa" , "Native African language" , "Group of widely spoken languages of southern Africa" .)