The EU on Thursday stepped up warnings that countries could be punished if they fail to share the burden of mainly Syrian refugees stranded in Greece and Italy.
Migration Commissioner Dimitris Avramopoulos said member states had until September to take in 160,000 Syrian and other refugees from the two countries, which have been on the frontline of the migration crisis.
So far only 13,500 have been relocated in a process bogged down by general inertia and resistance from Eastern European states which oppose Muslim immigration.
"If we don't have tangible efforts by September... the commission will not hesitate to make use of its power," Avramopoulos, who is Greece's EU commissioner, told a news conference.
The EU has been trying to convince members states "to do their duty," he said.
"But if it is not the case in the future, infringements might be an option," he said.
As the executive branch of the 28-nation EU, the European Commission is able to launch "infringement proceedings" to impose fines on member state that break the bloc's rules.
Countries like Hungary and Slovakia have proposed paying "solidarity" contributions instead of actually taking in any migrants.
But others such as France and Germany insist that no country can shirk its duty to admit a minimum number of refugees under the plan, which was pushed through in September 2015.
The EU launched the scheme 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.
In February, EU vice president Frans Timmermans said the Commission was for the first time considering penalties for states that break the rules.
Meanwhile the Commission urged EU nations to quickly seal deals with Nigeria and Tunisia to speed up the deportation process.
The EU says most African migrants are heading to Europe for economic reasons, making them ineligible for protection like that granted to asylum seekers fleeing war or persecution.
"We want to continue to offer succour to persons in need of international protection," Timmermans said in a statement.
"We owe it to them, to our partners outside the EU, and to our citizens to be able to say clearly: when in need, we'll help, when not, you must return."