Little louse is up for a passive protest (3-2)
I believe the answer is:
sit-in
'a passive protest' is the definition.
(I've seen this in another clue)
'little louse is up' is the wordplay.
'little louse' becomes 'nit' (I've seen this in another clue).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'nit'+'is'='nitis'
'nitis' written backwards gives 'SIT-IN'.
'for' is the link.
(Other definitions for sit-in that I've seen before include "Industrial action" , "Form of civil disobedience" , "Type of protest" , "Occupation of a place as a protest" , "Occupation of building as form of protest" .)