Choose not to participate (3,3)
I believe the answer is:
opt out
'choose not to participate' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for opt out that I've seen before include "Decide not to participate" , "Choose to be excluded" , "Choose not to participate" , "Decline to participate" , "Choose not to do something" .)