Migrant crisis: Greece, Croatia and Italy face EU legal action
The European Commission says it has begun legal action against Greece, Croatia and Italy for failing to correctly register migrants.
It says the three failed to implement the Eurodac Regulation, which involves fingerprinting asylum seekers and registering the data within 72 hours.
The commission said it warned about the shortfalls two months ago.
It has also launched an infringement case against Hungary over its asylum legislation.
Hundreds of thousands of migrants have arrived in Europe in recent months, causing divisions among EU states.
Almost half a million people arrived in Greece between 20 July and 30 November but Greek authorities have only fingerprinted about 121,000 of them, according to the European Commission.
"The European Commission sent administrative letters to Greece, Croatia and Italy in October. Two months later, concerns have not been effectively addressed. The European Commission has therefore decided today to send Letters of Formal Notice to Greece, Croatia and Italy, the first step of an infringement procedure."
Italy and Greece have both called on EU states for more help to deal with the huge influx of asylum seekers, many of whom are fleeing war and poverty.
In Athens on Thursday, 4,500 migrants arrived from Greek islands and 3,000 arrived from the Macedonian border, where authorities have blocked them from travelling further north. Macedonia says it is only accepting migrants from Syria, Iraq and Afghanistan.
The BBC's Nick Thorpe in Athens said some are being accommodated at an Olympic kick box stadium and others at a former airport where the Greek army is erecting tents.
The Greek minister for migration, Jannis Muzalas, said new arrivals had to apply for asylum within 30 days or be sent home.
Speaking earlier, Italian Interior Minister Angelino Alfano said infringement procedures would be "unreasonable". "For the work we've done, the only thing we deserve from the EU is a thank you," he said.
Regarding Hungary, the commission said it was not satisfied with the response from Budapest regarding its concerns over tough new asylum legislation, which it said breached EU rules.
"As a consequence of these concerns, the commission has today initiated an infringement procedure and sent a letter of formal notice to Hungary," the statement said.
Hungary has been a major transit route for migrants, many of whom aim to continue on to Austria and Germany.
In September, it fenced off its border with non-EU Serbia to try to stem the flow of migrants, and a month later also closed its border with Croatia for the same reason.
New EU statistics released on Thursday showed that a total of 812,705 people had claimed asylum in the bloc in the first nine months of 2015.
A note on terminology: The BBC uses the term migrant to refer to all people on the move who have yet to complete the legal process of claiming asylum. This group includes people fleeing war-torn countries such as Syria, who are likely to be granted refugee status, as well as people who are seeking jobs and better lives, who governments are likely to rule are economic migrants.