The EU executive gave 13 member nations a two-month deadline Thursday to improve the fate of tens of millions of laying-hens confined in cramped cages.
The European Commission listed countries failing to comply with animal welfare rules as Belgium, Bulgaria, Greece, Spain, France, Italy, Cyprus, Latvia, Hungary, the Netherlands, Poland, Portugal and Romania.
One out of seven laying-hens in Europe -- or 47 million of 330 million-- are kept in tiny cages no bigger than a standard piece of typing paper.
Under a 1999 law that came into force on January 1, egg-laying hens must be kept in so-called "enriched cages" providing "extra space to nest, scratch and roost."
The European Union legislation states hens must be given at least 750 square centimetres of space -- which is not much larger than a piece of A4 paper -- "to satisfy their biological and behavioural needs."
"Full compliance with the requirements of the Directive by Member States is essential," the Commission said in a statement.
"It is clear that member states who don't fulfil their legal obligations not only create consequences on animal welfare but can also cause market distortions and unfair competition."
The use of "un-enriched" cages puts businesses that invested in complying with the new measures at a disadvantage.