It was unclear whether the commission had planned to go ahead with the legal action, which centres on the “right to reside” test that European Union migrants must pass before they can claim benefits in this country.
However, The Sunday Telegraph has now been told that the lawsuit will be lodged “shortly” in the European Court of Justice.
With European elections held in Britain on May 22, the timing of the lawsuit, over such an emotive issue, threatens to be incendiary.
Anger over the lawsuit will be compounded by the admission that Britain will give an extra £800 million to the EU budget this year because this country’s economy is outperforming other member states.
The European Commission said it was bringing its legal case because the “right to reside” test is discriminatory since British citizens do not have to pass it.
The test, first introduced by Labour to try to calm fears of so-called “benefits tourists” coming to the UK, requires migrants from other EU states to prove they are seeking work before they can claim benefits such as Jobseeker’s Allowance.
If Britain loses the case it will either have to change the law or face multi-million pound fines for non-compliance with EU rules.
The action is being brought by the office of Laszlo Andor, a Hungarian socialist and European commissioner in charge of employment and social affairs.
A spokesman for his office said the legal action would probably be lodged “shortly”.
“We expect the referral to the court to happen within the next three months,” the spokesman said.
“UK nationals have a ‘right to reside’ in the UK solely on the basis of their UK citizenship, whereas other EU nationals have to meet additional conditions in order to pass this ‘right to reside’ test.
“This means that the UK discriminates unfairly against nationals from other member states.
“This contravenes EU rules on the coordination of social security systems which outlaw direct and indirect discrimination in the field of access to social security benefits.”