The government's financial intelligence agency has examined the ATM systems of Commonwealth Bank's rivals and is confident they have not had the same problems in reporting large cash transactions to authorities.
Austrac, which is alleging systemic breaches of anti-money laundering laws by CBA, on Friday also said it did not "take lightly" its unprecedented legal action against the country's biggest bank.
"It's not something we take lightly, obviously," acting Austrac chief executive Peter Clark said before a Senate estimates hearing.
"We give very careful consideration to what measures we seek to apply in terms of addressing non-compliance, particularly if it's of a serious nature. So, a lot of careful consideration was given before filing civil penalty proceedings in this case."
Austrac had other "enforcement options" available to it outside of civil penalties, such as enforceable undertakings, he said.
Mr Clark also confirmed the agency had looked at intelligent deposit machines (IDMs) - which can accept deposits - across the industry, before launching its action against CBA.
Banks must report individual cash deposits of more than $10,000 to Austrac, but the agency has alleged CBA failed to do this on more than 53,000 occasions between 2012 and 2015, and that it also failed to report or monitor other suspicious behaviour.
"We undertook an examination of ... the major banks in terms of their intelligent deposit machines," Mr Clark said.
"We were satisfied that they [the other major banks] had thresholds less than the reporting threshold for their transactions, and they have in place mechanisms to monitor and report."
Unlike rivals, CBA's IDMs can accept cash deposits of up to $20,000. National Australia Bank and ANZ Bank cap cash deposits into their machines at $5000, while Westpac imposes a $4000 limit per transaction.
The seriousness of the allegations against CBA were also underlined by Fitch Ratings, which on Friday said it would be looking at the bank's legal defence to examine if the evidence pointed to wider failings or cultural problems.
For the bank's credit rating to be affected by the scandal, Fitch said there would need to be evidence of wider flaws in its risk management framework, or a damaging fine.
Responding to the allegations, CBA has said it is possible that more than 53,000 failures to report large transactions could be treated as one contravention of the law, because they were caused by the same coding error.
Each contravention carries a maximum penalty of $18 million, so such an interpretation would greatly reduce any potential fine for CBA.
Mr Clark said the court would determine the size of any fine, taking into account factors including the number of alleged contraventions.
"The Federal Court will take into account a range of issues when considering penalty, and that will obviously go to the size of the number of contraventions, the totality of the alleged behaviour and so forth," he said.
Mr Clark was also asked by senators about when, or if, Austrac had informed senior ranks of CBA about the investigation into the bank. The corporate watchdog, ASIC, last week said it would look into whether the bank had properly disclosed the risk to investors.
Mr Clark said he could not answer such specific questions because of the court case, though he did say his agency had "quite a lot of engagement" with CBA over the matter.
