Company facing start of military strike action (6)
I believe the answer is:
combat
'action' is the definition.
(combat is a kind of action)
'company facing start of military strike' is the wordplay.
'company' becomes 'co' (abbreviation).
'facing' is a charade indicator (letters next to each other).
'start of' says to take the initial letters.
'strike' becomes 'bat'.
The initial letter of 'military' is 'm'.
'co'+'m'+'bat'='COMBAT'
(Other definitions for combat that I've seen before include "Battle or fight" , "Military fighting" , "War; contest" , "Military action" , "Armed fighting" .)