LUXEMBOURG • European Union (EU) countries cannot imprison illegal migrants just for crossing borders inside the passport-free Schengen area, the bloc's top court has ruled, delivering a new blow to efforts to crack down on the migration crisis.

The European Court of Justice in Luxembourg said yesterday that EU rules prevent the jailing of non-EU migrants who have illegally crossed a frontier if they have not already been subject to deportation procedures.

The ruling came in the case of Ghanaian woman Selina Affum, who was caught by French police at the Channel Tunnel while on a bus from Belgium to Britain using someone else's passport. French police placed her in custody for illegal entry to France and then asked Belgium to readmit her.

The EU court, ruling on Ms Affum's appeal against her detention, said that it was against the EU's "return directive", or laws on deporting migrants.

"The return directive prevents a national of a non-EU country who has not yet been subject to the return procedure being imprisoned solely because he or she has entered the territory of a member state illegally across an internal border of the Schengen area," it said.

The Schengen passport-free area of 26 European countries has come under severe pressure from the continent's biggest migration crisis since World War II. Faced with an an influx of more than one million migrants and refugees over the past year and a half, many Schengen countries have brought back border controls that were dismantled a decade ago.

Aiming to offer legal paths to Europe for migrants and to fill skills gaps in the labour force, the EU Commission has proposed easing access to the EU job market for qualified foreigners. The commission wants to reinvigorate its Blue Card scheme - akin to the Green Card in the US - which has failed to gain widespread use.

As well as lowering the minimum salary that jobs must offer before being open to Blue Card applicants, the proposals would extend eligibility to some of those who have arrived irregularly in Europe and are now seeking asylum.

"Early and effective integration of third-country nationals is key to making migration a benefit for the economy and cohesion of our society," Migration Commissioner Dimitris Avramopoulos said.

The scheme is aimed at highly qualified workers who get a job offer in the EU, with the minimum duration of the contract halved to six months from 12.

The commission wants to lower the scheme's salary threshold to make more jobs available. At present, Blue Cards are issued only to skilled professionals earning 50 per cent more than the average.

EU states would still be allowed to decide how many people they want under the scheme.

The commission said the scheme would benefit the bloc's economy. It said migrants had considerably lower employment rates compared with host-country nationals.

"The short-term impact on growth is mainly driven by additional spending, while labour market participation is expected to be key in determining the impact in the medium to long term," it said.

AGENCE FRANCE-PRESSE, REUTERS