The corporate regulator has launched legal action against National Australia Bank for allegedly manipulating the bank bill swap rate (BBSW) 50 times. NAB said it would fight the case.

Labor leader Bill Shorten jumped on the move, saying it provided further evidence of the need for a royal commission into the banks.

APRA has recognised that the shadow banking sector relies on the big banks. Credit:Bloomberg

"How many more people need to suffer and get ripped off before [Prime Minister Malcolm] Turnbull stops covering up for the banks?" Mr Shorten said.

"Rather than hold the big banks accountable, Mr Turnbull is gifting them a $7.4 billion tax handout. It is an insult to everyone who's been ripped off. Mr Turnbull has a choice here - and he's putting the big banks first. He's governing for the banks, not the Australian people."