The fine was imposed for concluding an agreement containing disallowed provisions on minimum prices that was in force for nearly four years, AZTN said in a statement.
The resale price maintenance arrangement in question prohibited NTL from selling Kras products below certain pre-agreed price levels, AZTN said.
AZTN is fining Kras 1.56 million kuna while NTL's penalty is set at 1.02 million kuna.
In a bourse filing, Kras said it would appeal the fine.
NTL was set up by some of the minor grocers in Croatia to better compete with their bigger rivals.
(1 euro=7.6653 Croatian kuna)