Leaders from the Czech Republic, Hungary, Slovakia and Poland rejected on Tuesday what they called Brussels' use of "blackmail and diktat" over planned resettlements of migrants across the EU.
Long opposed to sharing the burden of hosting mainly Syrian refugees, the four eastern EU states ruled out any links between accepting them and future disbursements of EU funds.
Eastern EU states "will never accept blackmail and diktat" on migration policy, Polish Prime Minister Beata Szydlo said at a press conference in Warsaw with her Czech, Hungarian and Slovak counterparts.
Czech Prime Minister Bohuslav Sobotka insisted that all four countries "oppose linking the debate about migration to European funds."
"This is blackmail, that we reject in the name of the Slovak government," added Slovak Prime Minister Robert Fico.
EU members have until September to take in 160,000 refugees from Syria and elsewhere currently living in Greece and Italy, which have been on the frontline of the migration crisis.
So far only 13,500 have been relocated in a laborious process that has been bogged down by resistance from central and eastern European states that oppose Muslim immigration.
This month, the EU warned that countries could be punished if they fail to share the burden, raising the possibility of fines on member states.
The EU launched the relocation scheme in September 2015 to deal with the biggest wave of refugees in its history, with more than 1.1 million arriving in 2015, most of them fleeing the conflict in Syria.
Hungarian Prime Minister Viktor Orban said at Tuesday's press conference that Budapest was ready to start detaining asylum seekers in camps on its southern border with Serbia, a plan that has drawn criticism from rights groups and the UN.
"From now on, Hungary is in a position to react even if the agreement between the EU and Turkey does not work. We are able to stop any wave of migrants on the Serbian-Hungarian border," he said.