Counter work by model (6)
I believe the answer is:
oppose
'counter' is the definition.
(thesaurus)
'work by model' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'by' is a charade indicator (letters next to each other).
'model' becomes 'pose' ('pose' can be a synonym of 'model').
'op'+'pose'='OPPOSE'
(Other definitions for oppose that I've seen before include "'Refute, stand against (6)'" , "Actively resist" , "Resist (someone)" , "Resist; play against" , "Bar" .)