"In addition, we expect dividends to reduce by a commensurate amount," it said.
The arbitration was in relation to Fonterra's precautionary recall in 2013 of a particular whey concentrate commonly used in infant formula and sports drinks.
The decision to recall was based on incorrect third party information that indicated a potential botulism contamination.
It was subsequently confirmed that there was no food safety risk to the public.
"In our opinion, the events are not indicative of any failing of corporate governance and we believe that Fonterra has appropriately addressed its food safety monitoring processes," S&P said.
S&P rates Fonterra's long term debt at A minus, with a stable outlook.