Herculean task for governing party (6)
I believe the answer is:
labour
'party' is the definition.
(Labour Party is an example)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for labour that I've seen before include "21 [PARTY] ?" , "Left - work" , "Productive work" , "Donkey-work" , "Hard work, party" .)