A global anti-corruption agency has accused Australia of delaying action on tax evasion by failing to sign an early information swap treaty - part of its commitment to the G20.
Transparency International advocates for greater sharing of information between countries.
Senior program co-ordinator Maggie Murphy said it was disappointing Australia would no longer be an early adopter.
''If you're championing a process, if you're the leader of this group of nations, and you're at the same time saying we need an international body to take things forward, then you need to be part of that drive forward,'' she said.
Australia chairs the G20 and will lead discussions on tax evasion and profit shifting in Brisbane in November.
The tax-swap agreement was endorsed by finance ministers at a G20 meeting in Sydney in February. It will see authorities share private information on bank accounts and other financial assets every year as part of the global crackdown on tax dodging.
So far, more than 40 countries have signed up to the program, including developed countries such as Germany and Britain, and tax havens such as the British Virgin Islands. Australia has not signed, despite taking a leading role in countering tax evasion.
Treasury is believed to be stalling over compliance costs to have more time to consult business.
Finance Minister Mathias Cormann declined to comment.
Ms Murphy said any extended consultation with business could diminish trust in Australia at the G20. ''If [there is] a behind-closed-doors discussion then I think they're going to lack the trust from other stakeholders,'' she said.
A joint statement by signatories to the agreement said it was a ''step change in our ability to clamp down on tax evasion, which reduces public revenues and increases the burden on those who pay their taxes''.