Suncorp has claimed that the Financial System Inquiry has "made the major banks nervous".
Chief executive Patrick Snowball said the big four banks are uncomfortable with the attention that has been paid to the fact they have less stringent capital requirements than the non-majors.
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"We fundamentally don't think it's in the best interests of consumers that major banks hold up to a third less capital than the regional banks over mortgage portfolios with the same risk profile," he said.
"Or that they receive a better deal on funding because of the government's implicit guarantee – which ultimately comes at the expense of taxpayers."
Mr Snowball, who was speaking at the American Chamber of Commerce, said it would be a "huge lost opportunity" if the federal government failed to address the issue.
He said a "competitively neutral capital regime" would benefit the Australian economy.
"Improved competition in the low-risk housing market will deliver increased pricing tension and better value for customers," he said.
"Similarly, with lower capital requirements, regional banks will have more capital to lend to the SME market or invest in innovation and product development across all portfolios."
[Related: Suncorp reduces variable rate to 4.69pc]