The European Commission is preparing to investigate David Cameron’s immigration crackdown to determine whether it is legal under EU law.

In a challenge to the UK Government the Commission said the Prime Minister’s plan to halve the amount of time foreigners can claim benefits will be assessed to check if it amounts to an “abuse” of the current EU immigration laws.

The coalition will introduce laws to ensure European Union migrants can only claim for work benefits for three months instead of six.

Writing in The Telegraph, the Prime Minister pledged that he would also stop more than 500,000 British jobs being advertised across the UK and announced tough new curbs on colleges offering visas to bogus students.

Mr Cameron said the changes will change the immigration system so it puts “Britain first” and ensure the UK is a “country that is not a soft touch”.

“We changed the rules so that no one can come to this country and expect to get out-of-work benefits immediately; they must wait at least three months.”

However European Commission officials have warned that they intend to assess whether they new policy complies with EU rules.

European Commission official told The Telegraph: “As and when Britain has finalised we will assess compliance with EU rules. There are strong safeguards in EU law against abuse. The vast majority of EU migrants going to other EU member states are going there to work and are net contributors.

They added: “There’s no legal obligation for Britain to advertise the jobs. The first people that will be harmed will be British businesses, they’ll be handicapped”

An official spokesman for the commission added it was “difficult to comprehend the announcement.”

“As and when these proposals are finalised properly, we will scrutinise them carefully to see if they are fully compliant with EU law.”

In February the Commission started a furious row with Westminster after claiming that Cameron’s plan to ban foreign migrants from receiving benefits unless they earn a minimum of £149 a week are illegal.

The Commission threatened to take the British Government to court after claiming it was illegal to define a “worker” according to the amount he or she earns is not compatible with EU law.

A source close to Iain Duncan Smith, the Work and Pensions Secretary hit back: “We’re absolutely confident the changes are legal as well as right.”