Economists predict the Official Cash Rate will rise today, but opinions differ on whether it'll be a 25 basis point increase, or 50.

Mortgage advisory firm Squirrel Chief Executive, David Cunningham, has penned an open letter to the Reserve Bank Governor saying they shouldn't lift the OCR.

He says the effects of measures already taken are still unrolling.

He told Kerre Woodham his letter is born out of a frustration over economists accepting interest rates must rise more.

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