Sanctions could include cutting funds, extending the monitoring of the judicial system or blocking membership of the Schengen passport-free zone.

ECONOMIST: Romania in trouble

Over the past year the Danish, French and Italian governments have rolled back the Schengen passport-free zone and reintroduced limited border controls.

ECONOMIST: Immigration

Mr Tusk just about accuses his fellow EU leaders of hypocrisy for talking of integration and yet undoing the Schengen passport-free zone by reimposing some border controls.

ECONOMIST: Charlemagne

In September 2010, the EU again called on Bulgaria to take urgent action to tackle crime and corruption, and later in the year France and Germany announced that they would block Bulgaria from joining the Schengen passport-free zone until the country had made "irreversible progress" in this area.

BBC: Bulgaria profile

Another big task is meeting European Union worries about the rule of law, which are holding up Romania's accession to the Schengen passport-free travel zone.

ECONOMIST: Romanian politics

Germany says it will not allow Bulgaria or Romania to join the EU's passport-free Schengen zone if the issue is put to a vote in the EU on Thursday.

BBC: Germany mulls Schengen veto on Bulgaria and Romania

Germany said on Sunday it would veto any attempt to allow Bulgaria and its neighbour Romania to enter the passport-free Schengen zone when EU ministers discuss the issue later this week.

BBC: Bulgarian gang boss Evelin Banev's daughter kidnapped

It is hard to see what concessions might turn a No into a subsequent Yes: the only conceivable new opt-out is from the Schengen frontier-free travel zone, and that would break up the long-established Nordic passport union.

ECONOMIST: Denmark and the European Union: Still an odd man out? | The