Health NZ is standing by its processes, despite upset over staff having to pay back money received in error.

The Nurses' Union is raising concerns over the pay back request, as Health NZ still owes workers $2 billion in under payments.

HNZ Chief People Officer Andrew Slater says at any one time, only about one million in errors is being chased across a $10 billion pay roll.

"This is just us making sure that people are paid accurately - and we are working with taxpayer money wisely."

Slater says they're incredibly frustrated at what it owes workers, and they're working round the clock to fix this.

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