After mid-July lad joins a corporation for final say (9)
I believe the answer is:
ultimatum
'final say' is the definition.
'after mid-july lad joins a corporation' is the wordplay.
'after' is a charade indicator (letters next to each other).
'mid' indicates the central letters.
'lad' becomes 'tim' (**).
'joins' says to put letters next to each other.
'corporation' becomes 'tum' (I've seen this before).
The centre of 'july' is 'ul'.
'ul'+'tim' is 'ultim'.
'ultim'+'a'+'tum'='ULTIMATUM'
'for' acts as a link.
(Other definitions for ultimatum that I've seen before include "Final demand or statement of terms" , "A final demand - or else" , "Final (peremptory) demand" , "Final point" , "Final proposition or demand" .)