Sepp Blatter's plans to introduce a quota on the number of foreign players each team could field, have been condemned as "unacceptable" by the European Commission.

The Fifa president has been determined to implement the first part of his "six-plus-five" rule by the 2012-13 season and his vision appears to be a step closer following the overwhelming backing at Fifa's annual congress in Sydney.

However, despite Fifa's findings, the Commission has stepped in to warn that the plan would amount to discrimination.

"The European Commission is showing a red card to the six-plus-five rule," Vladimir Spidla, Europe's commissioner for equal opportunities, said. "This would be direct discrimination on the basis of nationality, which is unacceptable. It's a non-starter.

"Professional football players are workers, therefore the principle of non-discrimination and the right to free movement apply to them. If EU Member States allowed the application of the six-plus-five rule they would be in breach of EU law and players who are discriminated against could take the Member States to court. And they would win."

Reijo Kemppinen, head of European Commission in London, said: "European footballers have a right to work in any EU country, just like the rest of us. We would love to see more English players in Spanish La Liga or Italy's Serie A, for example."

In recent weeks Michael Platini, the Uefa president, had raised concerns that plans for a quota system may not be legally sound but Blatter had insisted Fifa would proceed "within the limits of the law". Fifa's plans are different to Uefa's proposals which defines home grown players as team members who, regardless of age or nationality, have been trained by their club or by another club in the National Association for at least three years between the ages of 15 and 21.

On Uefa's plans, Commissioner Spidla said: "Uefa's system of home grown players would not lead to direct discrimination based on nationality. The European Commission has conducted a study on the issue as a follow-up to the White Paper on Sport in July 2007.

"The objectives of the rule proposed by Uefa, such as the promotion of training young players and reinforcing the balance of competitions appear to be completely legitimate objectives in the general interest of all. It is to be celebrated that Uefa has adopted an approach which respects the principle of free movement of workers when it is working to promote the training of young European players.

"Still, there is a risk of indirect discrimination based on nationality because it is often easier for young national players to have access to training facilities in a club in a Member State than for players arriving from other Member States.

"It is also worth noting that the UEFA rule will only be fully implemented from the 2008/2009 season, when 8 of the 25 A-Team players (players eligible to be on the match sheet) must have been locally trained. In order to be able to assess the concrete impact of the UEFA rule regarding the free movement of workers, the Commission will conduct a new analysis in 2012.

"Finally, I would like to express my gratitude for the constructive dialogue which has been established between the Commission services and the representatives from the world of football regarding the question of "home grown players".

"My intention is to follow up and to strengthen this dialogue because I am convinced that it will be a significant help to us in the future."