An alliance of 183 organisations from 42 countries today issued a plea to world leaders to impose a tax on financial transactions to help meet the costs of the economic crisis and support developing nations.
The group amounts to the largest coalition yet to give its backing to an international financial transactions tax, and includes members of the UK-based Robin Hood Tax campaign including the TUC, Friends of the Earth and ActionAid.
Their plea comes ahead of the summit of leaders of G20 economic powers in the South Korean capital Seoul on November 11-12, when measures to stabilise the world economy and boost the recovery will be high on the agenda.
Today's letter, addressed to G20 leaders including Prime Minister David Cameron and US President Barack Obama, is signed by development, health, education and environmental charities and unions from 16 of the G20 countries.
It says that a financial transaction tax would help meet the costs "of the global financial and economic crisis, including reducing the unacceptably high rate of job loss, and achieve key development, health, education and climate change objectives in developing countries".
TUC general secretary Brendan Barber said: "Governments around the world are embarking on a sweeping programme of austerity measures that will lead to huge job losses and cuts in services that the most vulnerable in society rely upon.
"At the same time the banks are back to business as usual with multimillion pound salaries being paid to the chief executives of bailed-out banks and billions handed out in bonuses.
"A Robin Hood Tax would mean the world's banks paying to reduce deficits they helped cause and would remove the need for such swingeing cuts in public spending."
Friends of the Earth's head of international climate Asad Rehman said: "Recent floods in Pakistan and droughts in Africa show the devastating reality of climate change on people in developing countries.
"A Robin Hood Tax on financial transactions is a crucial measure to help generate the minimum 200 billion US dollars (£125 billion) needed annually to begin tackling the problem."
Jenny Ricks, head of campaigns at ActionAid, said: "The G20 must now turn the global economic crisis into an opportunity to help the world's poorest. A tiny tax on the banks could raise hundreds of billions needed for those around the world feeling the effects of a crisis they did the least to create."