Medical aid charity Médecins Sans Frontières (MSF) says it will no longer take funds from the European Union in protest at its migration policy, reprts BBC News.
MSF singled out the EU's deal with Turkey under which Turkey agreed to take back any migrants who crossed the sea to Greece in smugglers' boats.
The number of migrants - many from war-torn Syria - to Europe is at its highest level since World War Two.
The charity received $63 million (£44m) from the EU and its members last year.
"MSF announces today that we will no longer take funds from the EU and its Member States in protest at their shameful deterrence policies and their intensification of efforts to push people back from European shores," the group said in a statement.
Jerome Oberreit, MSF's international secretary general, told a news conference that the EU-Turkey agreement went against the fundamental principles of providing assistance to people in need.
He said the deal did nothing to address the chronic deficiencies of EU policy, but simply outsourced European obligations.
"This is really about Europe's refugee shame," he said.
MSF said none of its patients would be affected by its decision on funding, and that in the short term it would cover the shortfall from emergency reserves.
The organisation receives 90% of its overall funding from private sources, not governments.
The EU-Turkey deal came into effect on March 20th.
Migrants arriving in Greece are now expected to be sent back to Turkey if they do not apply for asylum or their claim is rejected.
For every Syrian migrant sent back to Turkey, one Syrian already in Turkey will be resettled in the EU.
A month into the arrangement, EU officials said it had begun to produce results.
The International Organization for Migration (IOM) estimates that more than 1,011,700 migrants arrived by sea in 2015, though other agencies put that number much higher.
Most of the migrants take the relatively short journey from Turkey to Greece, though some leave from Libya, hoping to make it to Italy.