The email was highlighted by Ray Hadley on his morning 2GB programme, who criticised the bank's Youth Network for falsely claiming that 3000 suicides each year were LGBTIQ related.
It was sent to Westpac and St George bank employees and also claimed that voting 'Yes' was a “no brainer”.
“Along with ensuring all our colleagues and mates feel included and have equal rights, legalising SSM would prevent 3000 suicides per year,” the email read, according to Hadley.
“If Tony Abbott’s daughter is publicly voting 'Yes', so should you.”
The website states that in 2016, 2866 people died from intentional self-harm in Australia, the third highest suicide rate in the past ten years.
In 2016 suicide was the leading cause of death for the 15-44 age bracket, regardless of gender or sexual orientation.
When asked about the email a Westpac spokesman told SBS News the Youth Network "was a group of young, enthusiastic Westpac employees who get together to discuss a range of issues in an open way.”
The bank said the suicide link in the email was a “mistake”.
“We acknowledge that linking same-sex marriage and suicide may be inaccurately interpreted and we apologies (sic) for this mistake,” the spokesman said.
“A note will be issued to the Youth Network correcting this mistake”.
The spokesman said the email was sent to about a quarter of Westpac's total staff, all of which who were under 30 years old.
On Thursday morning Immigration Minister Peter Dutton weighed in on the email telling Westpac to “Stick to your knitting”.
Peter Dutton spoke out against the email on 2GB. Source: AAP
I don’t want sporting organisations or groups involved in delivering banking services telling us how to live our lives,” he told Ray Hadley.
Westpac told SBS News their support for marriage equality had not changed.
“However we understand there’s a range of views within any large organisation and we respect that. We are encouraging our employees to have their say, and we’re not telling them what to say.”
If you or someone you know is struggling mentally call Lifeline Crisis Support on 13114 or visit .
