Bankwest will close its remaining east coast branches and reduce trading hours in regional Western Australia as more customers go online.
Fourteen branches will shut by the end of October, five each in NSW and Victoria, three in Brisbane and one in Adelaide.
A further 29 branches in regional WA will shift to only trading two to four days per week, the Commonwealth Bank subsidiary confirmed on Tuesday.
The move is expected to impact about 120 staff, who will be offered redeployment opportunities.
Executive general manager Jason Chan said east coast branches averaged about 25 transactions per day, down 64 per cent in five years.
He said digital app usage had risen significantly over the same period.
"Bankwest is in a strong position to grow as a homeowner-focused digital bank on the east coast due to our distinct brand, first-class broker offering and 24/7 digital and contact centre services," Mr Chan said.
"We have a clear ambition to serve more home loan customers nationwide who are seeking simple, friendly and easy access to their banking services through their mobile phone or tablet device."
He said customers would still be able to carry out their day-to-day banking at post offices.
Finance Sector Union national secretary Julia Angrisano accused Bankwest of "abandoning customers and communities".
"The major banks are so obsessed with profits that they have lost sight of their responsibility to the community to provide financial services," she said in a statement.
"They act without any concern for their customers and dump them without a second thought when profits at particular branches decline.
"The truth is that the banks are actively pushing customers into digital banking."
The union wants a federal inquiry into the impact of bank closures, saying all Australians should be able to walk into a local branch.