Westpac is being urged to write-off overdrafts caused by a technology glitch

The bank is apologising - after MasterCard credit and debit payments made on December 22 and 23 did not go through.

The payments were suddenly withdrawn on Thursday night, leaving some unwitting customers hundreds of dollars in debt.

Westpac says any overdraft fees and interest will automatically be waived.

But Nga Tangata Microfinance's Natalie Vincent, who helps financially vulnerable people, says the debts should be wiped.

She says it's cruel to leave people to start the New Year in this position - and because it's a bank error, they need to rectify it.