Argument about a bar’s latest set of charges (6)
I believe the answer is:
tariff
'set of charges' is the definition.
'argument about a bar's latest' is the wordplay.
'argument' becomes 'tiff' (I've seen this before**).
'about' is an insertion indicator.
'latest' suggests the final letters.
The final letter of 'bar' is 'r'.
'a'+'r'='ar'
'tiff' placed around 'ar' is 'TARIFF'.
(Other definitions for tariff that I've seen before include "List of fixed charges as in hotels" , "List of duties on imports or exports" , "Rate" , "Customs-duty" , "Export/import duty" .)