Jenee Tibshraeny: NZ Herald Wellington business editor on the Reserve Bank governor upping the ante against the major banks - Heather du Plessis-Allan Drive

Reserve Bank governor Adrian Orr has stepped up his verbal war against the big four banks.

It's been revealed Orr sent a letter using 'colourful' language to defend the amount of capital the Reserve Bank requires these banks to hold.

NZ Herald Wellington business editor Jenee Tibshraeny explains the issue further.

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