The last remaining bank branch in the Mandurah central business district will close its doors this month.
Westpac Mandurah will shut on August 26.
Westpac sent letters to customers last week announcing the closure.
Its Mandurah Forum branch will stay open.
A Westpac Group spokesperson said the move was the result of declining customer use of branches.
The Finance Sector Union (FSU) said the closing of bank branches had "reached a crisis point".
The Mandurah branch is just one of 27 bank branches across the country that will be shut by three of Australia's 'Big Four' banks over the next few months.
The four banks have closed more than 550 bank branches across Australia since January 2020, including several branches in Mandurah's CBD.
The union urged the government to intervene.
"We must act to stop the banks walking away from communities in our suburbs and towns," union national secretary Julia Angrisano said.
"It's time to examine the impact of these closures which have hit hundreds of communities across the country."
Ms Angrisano said for decades the major banks had been supported by the government but had failed to support local communities in return.
"Instead the banks continue to shut down branches, sack workers and turn their backs on customers and businesses.
"Cost savings from branch closures are designed to increase the banks' already huge profits," Ms Angrisano said.
The Westpac spokesperson said most staff would continue in roles within the Westpac Group.
"We have a robust process in place to assist employees to find new opportunities.. meaning the majority of employees affected secure a new role and continue their career..."
The spokesperson said Mandurah customers could access cash services locally via Australia Post at Mandurah East Post Office...
The bank had ATMs located at Mandurah Forum and customers could call to talk to a banker.
For those who are new to digital banking, or those requiring more assistance with the changes, the bank now provided dedicated support and education.
Ms Angrisano said the Australian Banking Association's commitment to consulting the community about proposed branch closures, was being ignored.
"We need an inquiry into bank branch closures to assess the impact on local communities when the banks pull out of suburbs and towns.
"The UK has a formal 'community impact assessment test' and we need a similar test to ring-fence our branches and make sure banking services the public which they derive their profits from."
Westpac Group is closing close 24 branches; CBA is closing five and NAB is set to close eight banks.