The bank said it was close to achieving gender pay equity in terms of men and women doing the same job being paid the same.
But deeper analysis of its gender pay gap showed the yawning distance between the median hourly pay of its male and female staff.
Westpac has put the gap down to a lack of women in middle to senior management and gender segregation with women dominating lower-paid customer service positions at the bank and more men working in higher-paid areas such as IT, finance and corporate banking.
Tali Williams, First Union's secretary for retail, finance and commerce welcomed Westpac's public admission but blamed the problem on low pay for customer service roles which are dominated by women.
"It's no secret that a number of New Zealand's major employers have a guilty secret – they aren't paying women fairly – and it's because their entry-level customer service roles are done predominantly by women, lowering the bottom of the wage scale," she said.
"We applaud Westpac for their transparency and proactivity, and we hope other banks will follow suit and report publicly about gender-based wage disparities in their workplaces – it's time customers and prospective employees know who they are supporting."
"However, we would place much more emphasis on the cause of the gender pay gap being low wages for the lowest-paid workers, many of whom are women in customer service roles."
The union had been in touch with Westpac over the figure and offered to work with the bank on the issue.
Williams said businesses shouldn't have to pay a lot of money to consultants to report on the issue.
"Public reporting should be required and enshrined in law."
In April 2018 Britain introduced a law requiring organisations with over 250 employees to publish their gender pay gap.
Of the 10,016 companies surveyed, 78 per cent of companies paid men more than women.
Iceland is hoping to close its gender pay gap after introducing a law requiring companies to pay men and women equally.
Since the start of 2018, every company with 25 or more staff must gain certification from an accredited regulator proving they pay their women and men employees equally.
Firms with between 25 and 90 employees have until the end of 2021 to prove their equal pay structure. Those who fall below standards will face a daily fine and public naming and shaming.
New Zealand's gender pay gap is 9.3 per cent across the board while the financial services sector has a gap of 23.7 per cent.
The union's call is being back up by Saunoamaali'i Dr Karanina Sumeo, Equal Employment Opportunities Commissioner, who called on the Government to make pay transparency reporting mandatory.
"Westpac is one of the first corporates in New Zealand to be really honest and transparent about their gender pay gap, and they are to be applauded for that.
"They used expert advice to look at their gender pay gap at every level of the business."
Sumeo said while Westpac's pay gap was much wider than the overall gap in New Zealand of 9.3%, the bank was now in a great position to work hard and close it.
"Not all businesses are prepared to be as transparent as Westpac, and that is why I call upon the Government to make pay transparency reporting mandatory."
Julie Anne Genter, minister for women, said her ministry had been researching how pay transparency worked in other countries.
"I look forward to progressing pay transparency further."
"The more women can see about pay, the more likely they are to be paid fairly."
But she did not put a timeframe on when that progress might happen.
Westpac hopes that by publishing its data it will encourage others to follow suit.
The Herald this morning sent requests to all the major banks asking about their gender pay gaps.
Kiwibank chief executive Steve Jurkovich says it doesn't have data but its gender pay gap is similar to Westpac. Photo/Doug Sherring.
Kiwibank CEO Steve Jurkovich said it didn't currently publish any data on the gender gap but it was an issue that its board had a "strong desire" for Kiwibank to deliver on.
"Like many in our industry Kiwibank's figures are pretty similar to what Westpac has revealed.
"We don't see the major challenge as pay equity – we have achieved that aim of paying men and women equally for doing the same job acknowledging that time in role and performance will have some impact for all roles and team members.
"The issue as we see it is, roles are not distributed equally between the genders – women are over-represented in some roles where the income is lower and senior roles tend to have an over-representation of men."
Jurkovich said he took the issue very seriously and the bank had changed its recruitment processes to help rule out unconscious biases and stereotyping.
It is targeting a gender split of 40/40/20 across all levels of Kiwibank by 2025 which meant all short-lists for recruitment had to have at least 40 per cent women.
The bank had also committed to putting a gender lens over all its policies, processes and strategies to rule out gender discrimination, will support flexible working for all employees and analysing its talent pipeline to address gaps.
Michelle Russell, general manager talent and culture at ANZ New Zealand said it didn't currently publish data but looking at the average salaries for men and women across the bank there was a gap of 21 per cent.
"But this closes – and in many cases favours women – when salaries are compared for like-for-like roles. We acknowledge there's an issue of representation of women in higher paying roles across the industry."
Russell said ANZ had lifted women in management roles from 32 per cent to 42 per cent in recent years. It also had initiatives to encourage women to stay with the bank and support them in progressing their careers into more senior roles.
"These include flexible working practices, market-leading parental leave support (last year we increased paid parental leave to 26 weeks, two years ahead of the extension becoming law), and contributions to KiwiSaver while our staff are on parental leave."
