Work hard for the party (6)
I believe the answer is:
labour
This clue is a double definition.
'work hard' is the first definition.
(I've seen this before)
'party' is the second definition.
(I know that Labour is a type of labor party)
'for the' is the link.
(Other definitions for labour that I've seen before include "Left - work" , "What mothers have been through" , "Workers" , "Workforce" , "women have expected for months to be in" .)