Securency International, which produces polymer banknotes, is being investigated by the Australian Federal Police over whether its agents paid kickbacks to foreign government officials.
Police did not specify the countries involved but they are believed to include Nigeria, Malaysia and Vietnam.
"We treat foreign bribe matters extremely seriously," a police spokeswoman said, adding that she was unable to discuss ongoing investigations.
The latest allegations come from an unnamed witness to the police probe, a former employee of Securency, who told journalists he kept a diary of instances of apparent misconduct.
On one occasion in 2007, a middleman hired by Securency told him he was going to bribe a central bank governor from an unnamed Asian country.
The following year the witness says a Securency colleague told him the company paid very high commissions to middlemen in Nigeria to ensure a contract to produce the country's polymer banknotes.
In another incident, a senior Securency manager told him to organise a female Asian "bodyguard", understood as a prostitute, for the deputy governor of a foreign central bank next time he visited Melbourne.