Fears have been raised that tighter regulation of the ancient hawala system of informal money transfers is harming the world's poorest economies.
Hawala is used in South Asia, Africa and South America
The secret, ancient and complex trade in goods and money is widespread in the Middle East and Asia.
The US has been seeking to regulate hawala traders, fearing it could be used by terrorist groups to move money around the world.
But some are now fearing that this could jeopardise billions of dollars carried across borders to support trade in developing countries.
"I usually send money to my mother every month," Anoor Hassan - a Somali trader in foodstuffs in Dubai - told BBC World Service's Assignment programme.
"If I don't send the bills, they don't get the food that they eat."
Within weeks of the 11 September 2001 attacks, US authorities had closed down al-Barakat - the Somali hawala group they claimed was funding al-Qaeda.
However, as Somalia has had no formal banking system for 13 years, the shutting down of al-Barakat was strongly criticised - Randolph Kent, the United Nations humanitarian representative in Somalia, has said it "is having a very, very serious effect".
"We are at a point where we have to start anticipating a crisis that could be unique in the modern state system - the collapse of an entire national economy," he added.
Hawala is quick, competitive and cheap - millions of foreign workers across the world use it to send money to their families.
There is no direct movement of funds. Instead, a system of complex swaps is employed, using food, fuel, electronics or gold as a way of balancing the books between operators - hawaladas - in different countries.
However, because it operated underground and with no proper records, American authorities were keen to introduce regulation into the system.
"Hawala is one of the important things that everybody needs to be focusing on," stressed Danny Glazer, Director of the US Treasury's Executive Office Of Terrorist Financing.
"We have to make sure that all methods for transferring money - particularly for transferring funds across borders - is covered by effective anti-money laundering and counter-terrorist financing regimes.
"What we're trying to do is make things harder for the terrorist financiers - to close down as many mechanisms for moving money as we can, to make it as expensive as possible, to make it as much of a paper trail as possible, to close down as many of the bad operators as possible, to make life as difficult for them as possible, and to disrupt their activities as much as possible."
Treasury Deputy Assistant Secretary Juan Zerati - the man behind the attempt to tackle the financing of terrorism - told Assignment that it was important to track "all potential mediums" through which money could flow.
"Certainly, in terms of hawala, we are concerned that any time you have a lack of transparency, a lack of accountability with respect to the movement of money, there is potential that medium can be used by terrorists and criminals," he said.
And he stressed there was evidence that al-Barakat had been "used by al-Qaeda to funnel money to some of its allies and to support its operations.
"We've seen case studies... that provides greater incentive for us to make sure the hawala system worldwide is regulated as well as being monitored."
To some extent this has already been successful.
Pakistan and the United Arab Emirates in particular have been pressing hawaladas to sign up for registration.
However, this regulation mission also touches on huge cultural sensitivities.
Dubai is the hub of much of the hawala trade
And some argue regulation is pushing up costs and making hawala too expensive - which will hit the world's very poorest.
Orthodox transfer services charge 10-15% of the amount to be sent, whereas hawalas charge only 1-3%.
They also offer better exchange rates and a wider delivery network.
Tens of billions are moved like this every year - funding a substantial proportion of world trade, and helping fund the economies of developing countries.
Partially, the controversy arises out of the fact that it is hard enough to estimate the scale of all hawala transactions - let alone the number, if any, that are linked to terrorism.
Intelligence services are wary about releasing details - but as far as is known the 11 September attackers used the normal banking system.
And Mohammed Jerda Hussain, the head of a loose collective of Somali hawala dealers, told Assignment that the hawalas he knows have been targeted needlessly.
"The governments, especially the US, have the right to monitor, and to try to regulate - but concerning the Somali hawala business, we really don't see anything that they could see as suspicious," he said.
"The sender and the receiver's families - most of them - their names are very similar.
"So really our mechanism is simple and transparent."
Mr Glazer stressed, however, that the US did not want to end hawala.
"It's not our goal to eliminate it," he said.
"It's our goal to make sure it's used in the right way, and there's some paper trails left, and it's operated in a transparent manner.
"Of course we would like to see alternatives to it, to the extent that it is not achieving those goals, and we're working with financial communities around the world to try to find ways to provide cost-effective money remittance services."