Tim Costello.

World Vision CEO Tim Costello said the tax symposium was 'clearly a business conference'. Photo: Luis Enrique Ascui

The Australian government accepted sponsorship totalling at least $US300,000 from three global accounting firms in exchange for seats at a high-powered G20 summit on countering corporate tax dodging.

A letter from the Treasury shows the government offered organisations sponsorship deals worth $US100,000 and $US50,000 in return for registered places and speaking roles at the G20 International Tax Symposium in Tokyo on May 9-10.

A Treasury spokeswoman said the event, hosted by Australia as president of the G20, was ultimately sponsored by Deloitte, PwC, KPMG and the Institute of Chartered Accountants Australia.

The letter, published online in US journal Tax Analysts, said sponsorship deals gave organisations an opportunity to ''shape the event'' and to take advantage of access to G20 and Organisation for Economic Co-operation and Development tax officials.

''Australia, as G20 president, will also invite senior G20 and OECD officials and tax administrators to the event, which will provide an excellent opportunity for your organisation to input into the G20 tax agenda in May,'' it said.

The deals have angered civil society groups that say they were outnumbered at the forum by representatives of the big three firms.

They also said it was unfair that the firms, which advise corporations on how to structure their tax affairs, had greater access to an event on countering tax avoidance by companies such as Google and Apple.

''It is inappropriate that Treasury has sold speaking spots and extra representation to companies that advise corporations on tax minimising - to a conference on tax reform,'' said Mark Zirnsak of the Tax Justice Network, which had two representatives at the event.

''It gave those firms over-representation in the consultation while there were only around five community representatives and as far as we are aware only 12 government officials from developing countries,'' he said. A Treasury spokeswoman confirmed Treasury received $US100,000 from each of the three accounting firms, as well as ICAA, to run the event. She said these organisations sent 50 delegates in total, out of the 230 that attended the forum.

''These firms have tax law experts and practitioners who are central to understanding the problem,'' she said.

''Without the financial contribution of these organisations we could not have hosted the symposium.''

According to the letter, Treasury gave the firms the option of becoming ''major supporters'' or ''valued supporters'' for either $US100,000 or $US50,000.

The ''major supporter'' package included six registrations, two speaking roles, an exclusive event such as a dinner, lunch or cocktail party, and the ability to make suggestions on panelist speakers. The ''valued supporter'' package included three registrations and one speaking role.

Tim Costello, chief executive of World Vision, who attended the event through the organisation's own funding, said civil society groups were ''thin on the ground''.

''It was very clearly a business conference,'' he said.

KPMG spokesman Ian Welch said the event would not have been possible without the organisation's sponsorship.

''It's a bit disappointing if groups are effectively criticising the people who made sure the conference was put on at all,'' he said.

''We certainly feel very strongly that we are a key part of this whole agenda and we've got insights to give and expertise to provide.''

Spokesmen for Deloitte and PwC declined to comment.

The G20 is leading a push by governments to crack down on the base erosion and profit shifting of multinational corporations.

Tax Commissioner Chris Jordan said at the event that Australia could be losing more than $1 billion in potential revenue each year because of the international tax-minimising strategies of multinationals.

The event was closed to media apart from opening and closing remarks.