A former Commonwealth Bank worker has lifted the lid on the "ruthless" tactics used by banks to prey upon vulnerable customers.

In a 60 Minutes program that aired on Sunday night, the whistleblower said staff were under intense pressure to sell products to customers, even those they suspected couldn't afford them, which contributed to a toxic workplace environment that forced her to end her career.

It comes as a banking royal commission unearths misconduct in the industry, including Commonwealth Bank advisers charging dead clients for financial advice, as well as providing loans to clients who were clearly unable to afford repayments.

The former staffer named Catherine, who began working with the Commonwealth Bank as a teller more than 30 years ago, told 60 Minutes she had seen the bank move its focus away from the customer and towards "pushing products" and sales.

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"Every customer that goes through the door, every customer that you serve, you are expected to see what products they have with you," Catherine said.

"You get to the stage where you see them come through the door and you think, 'Oh, what am I going to get out of this customer?'

"It makes me feel a little bit grubby. It's like we've all been tainted with this really bad taste. It's taken away the integrity."

Catherine described how staff were put under pressure to push products onto consumers to meet strict targets.

"A manager may get told, 'You need to have 20 home loans a week'," she said.

"Well, that means if you've got five staff, those five staff need to get four home loans each for the week. And so, Thursday comes around. If you haven't got them ... Friday can become a really, really hard day.

"There's some really ruthless staff that will get customers to increase credit cards, or do stuff. On paper they [the customers] may be able to afford it, but in reality you know that perhaps they can't."

You get to the stage where you see them come through the door and you think, 'Oh, what am I going to get out of this customer?'

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Julia Angrisano, the national secretary of the Finance Sector Union, said bank workers had reported being forced to act in ways that made them feel "uncomfortable".

"It was not uncommon for our members to tell us that their managers would expect them to peer over the counter and have a look inside the customer's wallet as they'd open up to have a look whether or not perhaps that customer had a credit card from one of its competitors," she said.

"We have many, many instances of members who tell us that they are so stressed before they go to work that they have to psych themselves up, and they're in their cars, crying, knowing what's about to happen when they walk through the door."

The banking royal commission has heard from bank customers who said they were on the brink of financial ruin after being pressured to take out loans, buy credit cards or take out insurance they didn't want or need, and struggled to meet repayments.

Katherine Temple, Senior Policy Officer for the Consumer Action Law Centre in Melbourne, told 60 Minutes the trouble some customers ended up in was "scary".

"A lot of people were in a lot of distress because they're loaded up with debt that they can't afford, and a lot of the times they never could afford," she said.

But Temple said people who struggled financially were actually very lucrative to banks.

"They are the ones who tend to pay the most interest, in late fees, in charges," she said.

"So there is an incentive there, I think, to provide loans to people who are living on the edge."

Another dodgy tactic revealed by 60 Minutes was banks forcing staff to sign deeds of non-disparagement before they left, which stopped them from speaking critically about their former workplaces.

Angrisano said the deed was valid "for life".

"Our view is certainly, about those deeds, is that it's just another form of control: 'We control you when you worked for us and now we're gonna control you once you even leave us'," she said.

The program aired after the Commonwealth Bank was forced to apologise for a Dollarmite scam that was unearthed by a Fairfax investigation.

The investigation revealed staff were depositing small amounts into children's Dollarmite accounts in order to make them appear active, in attempts to gain performance bonuses.

The Commonwealth Bank banned the practice after it was uncovered in 2013, the bank's chief executive Matt Comyn said.

"When customers open an account, they put their trust in us and that's particularly true when the account holder is a child," he said.

"There is now a line in the sand and we have zero tolerance for behaviour such as this, irrespective of whether there is customer harm."

Comyn said no "financial harm" came to the customers affected.

The next round of hearings of the banking royal commission, which starts today, is expected to hear from small business owners who were wronged by banks.