New Zealand's Commerce Commission has launched an investigation into whether major banks breached anti-cartel laws through their membership in the UN's Net-Zero Banking Alliance (NZBA), according to multiple media reports on Friday.

These include ASB and Bank of New Zealand, which are units of Commonwealth Bank of Australia (ASX:CBA) and National Australia Bank (ASX:NAB), respectively, as well as Rabobank, ANZ Group, (ASX:ANZ, NZE:ANZ) and Westpac Banking Corporation (ASX:WBC, NZE:WBC).

While ASB itself is not a member, its parent Commonwealth Bank of Australia is, while the Bank of New Zealand is a member of the alliance in its own right, the reports said.

The probe follows a complaint from Federated Farmers, alleging the banks coordinated lending practices, including uniform emissions reduction targets and reduced agricultural lending, which may potentially violate competition laws, the reports said.

The NZBA commits banks to align lending with net-zero emissions by 2050, raising concerns that such alignment may restrict farmers' access to finance.

The Commerce Commission is assessing whether the banks' climate commitments breach section 30 of the Commerce Act. The investigation's timeline remains unspecified, the reports added.