Join in support of European Issue (6)
I believe the answer is:
emerge
'issue' is the definition.
('emerge' can be a synonym of 'issue')
'join in support of european' is the wordplay.
'join' becomes 'merge' (I've seen this before**).
'in support of' means one lot of letters go next to another (I've seen this in other clues).
'european' becomes 'e' (abbreviation e.g. EU).
'merge' put after 'e' is 'EMERGE'.
(Other definitions for emerge that I've seen before include "Move out and become visible" , "Materialize" , "Gradually come out" , "Come to light" , "Come out or surface" .)