National Australia Bank faces a lawsuit from the corporate watchdog over a scandal involving its use of home loan “introducers,” in a landmark case that could attract a maximum penalty of more than $500 million.

In the latest sign of fallout from the banking royal commission, the Australian Securities and Investments Commission (ASIC) on Friday alleged the bank broke credit laws in relation to almost 300 loans. The alleged breaches attract a maximum penalty of $1.7 million to $1.8 million per breach, which adds up to a maximum penalty of more than $500 million.

NAB's introducer scheme is being targeted in a new ASIC lawsuit. Credit:Glenn Hunt

ASIC is suing NAB in the Federal Court over a scheme in which NAB paid lucrative commissions to real estate agents, lawyers, sports clubs and others in exchange for customer leads. The case follows last year's royal commission scrutiny of the "introducer" program, which was allegedly exploited by a bribery ring, in which bankers sold loans that were based on fake documents.

The regulator's deputy chairman Daniel Crennan, QC, said the maximum penalty under the law was "well beyond" the penalty a court would impose, although he said the case was highly significant.