Victoria's 2021 royal commission into the casino giant found Crown allowed patrons to gamble by depositing uncleared bank cheques made out in their names and not the company's.
Casinos can only accept cheques in limited circumstances under state laws.
The Victorian Gambling and Casino Control Commission has now ordered Crown to pay a $30m fine for the "serious contravention", adding that the practice subverted controls and was undocumented and long-running.
"This is the second time we've taken action on undocumented practices at the casino, and we will investigate further to ensure there are no more," commission chair Fran Thorn said in a statement on Thursday.
"To be clear, we will not allow the casino to conceal its practices to avoid scrutiny.
"Practices like accepting bank cheques expose Crown to the risk of money laundering, put patrons at risk of gambling harm, and compromise our ability to ensure the casino runs with integrity, safety and fairness."
Casinos have historically used cheques to minimise cash holdings, thereby reducing the risk of robberies and thefts in and around complexes.
But cheques carry risks, including the potential to exacerbate gambling harm and their use by criminals to launder money.
High-roller Ahmed Hasna, who has said he gambled at the Southbank casino almost every second day between 1993 and 2019, told the royal commission a bank cheque made out to him for $100,000 was initially honoured.
A short time later, the cheque was dishonoured and Crown took steps to recover the debt the problem gambler had incurred through the use of credited chips.
Mr Hasna was told by Crown he could continue gambling at the casino and maintain his highest-tier privileges as long as he repaid his $100,000 debt out of any future winnings.
"Leaving to one side the inexcusable issues associated with Crown Melbourne encouraging a gambling addict, who was already experiencing financial harm, to chase his losses and repay a gambling debt out of any future winnings, this example serves to demonstrate why it is that the use of cheques at the Melbourne Casino must be strictly controlled," the commission said.
The watchdog also probed royal commission findings that Crown likely accepted blank cheques in exchange for gambling chips, but has ruled there is insufficient evidence to establish the practice occurred.
Nevertheless, it will issue Crown directions to ban the blank cheque and bank cheque practices, conduct a review of its current bank cheque policies and procedures, and investigate undocumented practices at its Melbourne site.
A Crown Resorts spokesman said it would comply with the directions and work with the watchdog and Victorian government to address the issues and others stemming from the royal commission.
"Crown Melbourne accepts the outcome from the Victorian Gambling and Casino Control Commission," he said in a statement.
"These practices have ceased, and we have implemented significant improvements to reduce and prevent risk across our business. Under new ownership and leadership, our Future Crown program is driving whole-of-company reform."
It is the third time Crown has been fined following the eight-month royal commission, which found the company unfit to run the Southbank complex while giving it two years to reform itself.
Crown was last year hit with fines totalling $200 million for breaches of its responsible service of gambling standards and facilitating customers to illegally use their credit cards to access money.
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