The Australian Taxation Office (ATO) has pursued Karantzis for a $10 million tax bill, alleging he used tax havens to hide income, which previously prevented him from leaving Australia until December 2020.

After the ATO relaxed travel restrictions, Karantzis left for Cyprus, where he is now involved with a new company, ISX Financial EU.

In response to the suspension of trading, Karantzis filed a $500 million lawsuit against the ASX.

Karantzis has a history of business failures and legal disputes, including a notable case with Sugar Australia, where he faced accusations of misconduct.

Nickolas 'John' Karantzis, a controversial businessman, has been fined $1 million and banned from being a company director for six years due to a 'serious risk to the public', as determined by Justice Timothy McEvoy of the Federal Court in Victoria.

The corporate regulator ASIC found that Karantzis displayed a complete disregard for corporate regulations and compliance, contributing to his legal troubles.

The Australian Securities Exchange (ASX) suspended trading in his former company, iSignthis, which was ultimately delisted in November 2022 after its financial practices came under scrutiny.

iSignthis, now known as Southern Cross Payments, faces a $10 million penalty for breaching disclosure laws, with a deadline of 30 days to pay.

In September 2019, iSignthis had a market capitalization exceeding $1 billion, but within just three days, it lost over $800 million in value, significantly impacting Karantzis's wealth.

This dramatic crash was triggered by a report from Ownership Matters, which questioned the company's revenue targets and revealed that senior executives had awarded themselves over $500 million in shares.

Further investigations revealed that Visa terminated its relationship with iSignthis in May 2020 due to inadequate anti-money laundering practices, which Karantzis failed to disclose as required.