Join in support of European Issue (6)
I believe the answer is:
Here is my best explanation:
'issue' is the definition.
('emerge' can be a synonym of 'issue')
'join in support of european' is the subsidiary indication.
'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' after 'e' is 'emerge'.
(Other definitions for emerge that I've seen before include "Come forth or appear", "Come out or transpire", "Become known or apparent", "Break out (from an egg)", "Come to light", "Emanate", "Issue", "Become gradually apparent", "Come out or become known" and "Appear".)