Firm action reduced cocaine supply? (9)
I believe the answer is:
crackdown
'firm action' is the definition.
(I've seen this before)
'cocaine supply?' is the wordplay.
'cocaine' becomes 'crack' (crack is a kind of cocaine).
'supply?' becomes 'down' (I can't explain this - if you can you should believe this answer much more).
'crack'+'down'='CRACKDOWN'
'reduced' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
(Other definitions for crackdown that I've seen before include "severe action" , "Repressive action" , "Crushing measures" , "getting tough" , "Repression" .)