Very many backing call for industrial action (8)
I believe the answer is:
stoppage
'for industrial action' is the definition.
(I've seen this before)
'very many backing call' is the wordplay.
'very many' becomes 'pots' (pots can mean a lot of something).
'backing' says the letters should be written backwards.
'call' becomes 'page' (I've seen this before).
'pots' back-to-front is 'stop'.
'stop'+'page'='STOPPAGE'
(Other definitions for stoppage that I've seen before include "Deduction in wages" , "action by strikers" , "Onstruction in pipe or interruption in game" , "Deduction (from wage); cessation" , "sit-in" .)