Blue joke seen first gets severe action (9)
I believe the answer is:
crackdown
'severe action' is the definition.
(I've seen this before)
'blue joke seen first' is the wordplay.
I cannot quite see how this works, but
'blue' could be 'down' (I've seen this before) and 'down' is found within the answer.
'joke' could be 'crack' (a crack is a joke or quip) and 'crack' is found in the answer.
No letters remain.
This may be the basis of clue (or it may be nonsense).
'gets' is the link.
Can you help me to learn more?
(Other definitions for crackdown that I've seen before include "Firm action" , "severe action" , "Repressive action" , "getting tough" , "Repression" .)