Skittish banks have been closing what they consider high-risk accounts, many of them held by money transfer firms and humanitarian organizations, prompting the U.S. Government Accountability Office to open an investigation, the Wall Street Journal reported Saturday.

This week, the Journal detailed how such organizations have been forced out of the global banking system.

More than 50 nonprofits sent a letter to Treasury Secretary Jack Lew and Secretary of State John Kerry accusing banks and the Treasury of playing the blame game and doing little to solve the problem. They want the U.S. Treasury to state nonprofits aren’t inherently high-risk.

U.S. officials told the Journal they never intended for whole categories of customers to be blocked from the banking system. Rather, they wanted the accounts managed, not avoided.

“The GAO study will identify solutions to restore and expand humanitarian remittances and thus prevent further instability of Somalia and other vulnerable nations,” said Rep. Keith Ellison, D-Minn., whose district has the largest Somali population in the United States.

The acting undersecretary for terrorism and financial intelligence at the Treasury Department said last November it is unclear who is being cut off. “We don’t have a complete picture,” Treasury Undersecretary Adam Szubin said. “We still need more and better data.”

“Even large international NGOs [non-governmental organizations] are sometimes having trouble operating bank accounts if they’re trying to deliver aid to Syria, Afghanistan or Pakistan,” areas of particularly high risk for terror financing, Vijaya Ramachandran, an expert with the Washington think tank Center for Global Development, told the Journal.

The World Bank reported the closing of bank accounts of money transfer operators to prevent money laundering and combat terrorism has raised the cost of remittances, hiking some costs to 10 percent of the total being sent.

The result is that money is being driven underground, with companies forced to ship bags of cash overseas. More than half of 82 money transfer companies surveyed recently by the World Bank said they had lost bank accounts in 2014.

“Transactions that would have taken place legally and transparently may be driven underground,” Comptroller of the Currency Thomas Curry recently told an international conference of bankers and regulators in Washington.

“The whole flow of money goes underground, and that becomes counterproductive to the original purpose of being able to track [it],” said Dilip Ratha, head economist of the World Bank’s unit that studies remittances. “It’s a bit paradoxical.”