Banks must explain to customers why they are hiking up mortgage rates, the treasurer says, after two big players followed Westpac’s lead.

But according to Labor, the federal government also has some explaining to do, with its dysfunction facilitating the rises.

Commonwealth Bank and ANZ on Thursday became the latest major banks to lift their home loan interest rates, with both institutions blaming growing international borrowing costs.

Treasurer Josh Frydenberg said it was up to them to justify the move.

“Any financial institutional which makes these decisions needs to explain to its customers why,” he said on Thursday.

Labor finance spokesman Jim Chalmers says the banks are taking advantage of the chaos in the Liberal Party and knowing Scott Morrison will “always side with them over people who work and struggle”.

Australians have good reason to be frustrated with the big banks and will be taking their business elsewhere, he said.

“Middle Australia is already struggling to make ends meet and customers of the big banks will be considering other options.”

Westpac last week became the first major bank to reveal its variable home loan rates would go up, due to its wholesale funding costs rising.

Its variable home loan rates will go up by 14 basis points from September 19.

ANZ will lift its standard variable rate by 16 basis points from September 27 but the increase won’t apply to drought-affected regional customers.

CBA’s standard variable rate for owner-occupier borrowers will go up 15 basis points on October 4.