Mastercard has denied allegations brought by the consumer watchdog that it stifled competition by deterring clients from using EFTPOS.
In a brief hearing in the Federal Court on Wednesday morning, Mastercard's barrister Dr Ruth Higgins SC denied that the firm had an anti-competitive purpose as alleged by the ACCC.
"Mastercard will deny that it acted with a prohibited purpose of seeking to hinder EFTPOS' ability to compete," she told Justice Michael Wigney.
The Australian Competition and Consumer Commission filed the lawsuit in May, alleging that Mastercard misused its market power to prevent clients from properly choosing whether their debit card transactions would be processed by EFTPOS, Mastercard or Visa.
EFTPOS was typically the cheaper option, the ACCC said.
Dr Higgins denied that Mastercard's offerings were always more expensive, saying it brought other services such as fraud protection to its clients.
The firm's actions were for legitimate commercial purposes and did not negatively impact competition, she told the court.
According to the ACCC, Mastercard's conduct stemmed back to late 2017 as a response to the Reserve Bank of Australia's least cost routing initiative which aimed to increase competition and reduce costs for businesses.
Mastercard entered into contracts with 23 clients, including supermarkets, fast food chains and clothing retailers, in response to this, the commission said.
"We say that the strategy that was devised was to neutralise the incentive for those merchants to route to EFTPOS," said ACCC barrister James Arnott SC on Wednesday.
The ACCC is seeking penalties, costs and other orders in the case.