The European Commission is due to unveil options for reforms to the way EU countries handle asylum claims in response to the migrant crisis.
The move is in part a reaction to the difficulties faced by Greece and Italy to cope with thousands arriving from the Middle East and Africa.
Other countries meanwhile have taken in hardly any refugees.
Separately, people in the Netherlands are taking part in referendum on an EU free trade deal with Ukraine.
They will be given the choice of voting for or against ratification of the deal.
Correspondents say the non-binding referendum is being viewed by many as an opportunity to protest against the EU’s expansion and what they consider to be its undemocratic decision-making processes.
Some campaigners see it as a precursor of the UK’s June referendum on EU membership.
Under a Netherlands law from last year that created advisory referendums, the result is valid only if turnout is more than 30%.
If a majority votes against the deal, the government can introduce new legislation which in effect would cancel its ratification. Likewise if there is a vote in favour it can advise parliament to uphold the ratification.
EU Commission President Jean-Claude Juncker has described the stakes in the run-up to the vote as being high, warning that a “No'” vote could trigger a wider crisis in the 28-member bloc.
Flaws in the system
BBC Europe Correspondent Damian Grammaticas says that under the current system for dealing with migrants, known as the Dublin Regulation, countries have the power to return asylum seekers to the first EU state they entered for their claim to be dealt with there.
The British government is one of several countries that do not want to see wholesale changes to the system.
But the influx of more than a million people to Europe last year has made the flaws in the EU’s asylum system obvious, our correspondent says.
The arrangement whereby the EU country a migrant first arrives in must deal with their asylum claims has left some nations – especially Greece and Italy – battling to cope with hundreds of thousands of people seeking protection.
The European Commission is likely to suggest either a modest change that preserves the current system but adds a “fairness” provision so a country struggling to cope can get help, our correspondent says.
A second, more radical option would be to scrap the existing rules and distribute refugees around Europe.
However the UK and many eastern European states have made clear they want to keep the system which allows them to return asylum seekers to the country where they entered the EU.
Whichever proposal is finally agreed, our correspondent says, the UK cannot be forced to take asylum seekers as it has opt-outs from EU asylum policies.
Greece paused deportations of migrants to Turkey on Tuesday, a day after the first boats took back 202 people under a controversial EU plan to cut off a migrant route to Europe.
Hundreds more are due to be removed later this week, but the migrants are arriving in Greece faster than they can be sent back.
In other developments:
- Pope Francis is said to be considering a trip to Lesbos to highlight the difficulties faced by migrants and refugees there
- Germany may lift temporary border controls introduced last year to help reduce the migrant flow by mid-May if the number of arrivals continues to fall, the AFP news agency reported Interior Minister Thomas de Maiziere as saying
- Doctors Without Borders and Save the Children have suspended activities on several Greek islands to protest against the terms of the deal with Turkey. They argue that the deal turns reception centres for refugees into centres of inhumanity
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.