The tensions between some of Australia's largest banks and the uncompromising Apple Corporation have 'ratcheted up' over a banking app that allowed payments to be made via widely used chat applications - including those via iPhone - the AFR reports.The latest development marks a further souring in the relationship between the bank and Apple. It comes just three months after Westpac announced that, working with Israeli-based tech startup PayKey, it was offering banking options for messaging apps such as Facebook Messenger, WhatsApp and Snapchat. PayKey's keyboard app bridges the gap between bank applications and social networks by adding optional banking icons to the bottom of the screen during in-app conversations, according to online banktech news service Finextra.Westpac was one of a group of banks in Australia (along with Commonwealth Bank of Australia, National Australia Bank, and Bendigo and Adelaide Bank) which recently dragged Apple through a long-winded, and increasingly acrimonious battle with competition regulators over access to the iPhone's NFC chip, Finextra reminded its readers.Despite only being available for three months, the Financial Review understands the app  was installed by tens of thousands of customers.The bank declined to comment on the reasons behind Apple's decision, but sources told the Financial Review that Westpac had already addressed security concerns initially raised by Apple and had the app approved from that perspective. Other large banks in Europe and Asia have had similar applications approved by Apple for use in iPhones.The implication was raised that if the Westpac Keyboard is not a genuine security concern, Apple could be indulging in an anti-competitive move - that is, Westpac was stopped from letting its customers run payment keyboards on their iPhones because Apple wanted to launch its own payments keyboard and had been beaten to the punch. None of the major players involved would comment on the record.