Workers will be after material for officers (9)
I believe the answer is:
sergeants
'officers' is the definition.
(sergeant is a kind of officer)
'workers will be after material' is the wordplay.
'workers' becomes 'ants' (I've seen this before).
'will be after' means one lot of letters go next to another.
'material' becomes 'serge' (serge is a kind of material).
'ants' put after 'serge' is 'SERGEANTS'.
'for' acts as a link.
(Other definitions for sergeants that I've seen before include "Greatness among NCOs" , "Odd greatness of these army and police ranks" , "Greatness observed in NCOs" .)