Industrial action essentially to get capital (4)
I believe the answer is:
oslo
'capital' is the definition.
(capital of Norway)
'industrial action essentially' is the wordplay.
'industrial action' becomes 'go-slow' (when workers deliberately work slowly).
'essentially' says to take the centre.
The middle letters of 'goslow' are 'OSLO'.
'to get' is the link.
(Other definitions for oslo that I've seen before include "Nordic city" , "Capital city, called Kristiania until 1924" , "Northern city" , "foreign port" , "Capital often frozen" .)