Charlie follows old partner to work with justification (6)
I believe the answer is:
excuse
'justification' is the definition.
(excuse is a kind of justification)
'charlie follows old partner to work' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'follows' is a charade indicator (letters next to each other).
'old partner' becomes 'ex' (I've seen this in other clues).
'to work' becomes 'use' (I've seen this before**).
'c' after 'ex' is 'exc'.
'exc'+'use'='EXCUSE'
'with' is the link.
(Other definitions for excuse that I've seen before include "Defence, justification" , "Absolve" , "Forgive - allow to pass - plea" , "Upstanding community members" , "Cop out" .)