Apart from the interchange fee cap,
the Law regulates the following

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Co-badging – meaning a single device, e.g. a card, a smartphone or other devices may contain different payment means or brands (e.g. Visa, MasterCard, Maestro)
Unblending – more transparency in fee payment when acquiring banks offer and charge payees (such as merchants) individually for different categories and different brands of payment cards and not impose a single ‘blended’ fee.
Honor All Cards Rule – merchants are able to choose cards they want i.e. those with lower costs. For example, if a merchant accepts debit cards, he/she is not obliged to accept credit cards.
Illicit influence on merchants when it comes to choosing payment methods - Banks and payment schemes cannot prohibit merchants to direct customers towards using the payment method with lower fees and inform the customer of those fees.
Source: National Bank of Serbia