Argument about a right scale of penalties (6)
I believe the answer is:
tariff
'scale of penalties' is the definition.
'argument about a right' is the wordplay.
'argument' becomes 'tiff' (I've seen this before).
'about' indicates putting letters inside.
'a right' becomes 'ar' (I've seen this in other clues).
'tiff' placed around 'ar' is 'TARIFF'.
(Other definitions for tariff that I've seen before include "List of duties on imports or exports" , "Import or export duty" , "Customs-duty" , "Duty; table of charges" , "List of fixed charges as in hotels" .)