ASIC can't see bank culture: Bowen

Labor is pushing again for a royal commission into banks, saying the corporate watchdog can't determine their "cowboy" culture and contempt for business.

The opposition is bolstering its argument for a wider investigation after the Australian Securities and Investment Commission launched legal action against National Australian Bank "for unconscionable conduct and market manipulation".

"We are interested not only in the illegality but the culture which allows this sort of behaviour ... you see a contempt ... by people making key decisions on interest rates," shadow treasurer Chris Bowen told ABC radio on Wednesday.

The government dismissed the call as pre-election politics.

Finance Minister Mathias Cormann said ASIC was conducting its investigations with the same powers, if not more, of a royal commission.

"(It's) for political reasons, not because they think it's the right thing to do," he told ABC radio.

The government dismissed the call as pre-election politics.