Taranto, January 22 - A judge in the southern port city of Taranto on Tuesday upheld a request by local prosecutors to challenge the constitutionality of a 2012 law allowing the troubled ILVA steelworks to remain in production while much-needed environmental upgrades are carried out. The challenge will now be passed on to Italy's Constitutional Court. Prosecutors argued that the law, initially passed as a government decree before being converted by parliament, involved a conflict in the attribution of powers between the judiciary and the executive. Last week the court ordered the seizure of steel and semi-finished products from the plant pending the constitutional court ruling. The products, weighing in the region of 1.8 million tonnes and worth a billion euros, are currently lying on the company docks. ILVA has been at the centre of a political and legal battle since July when local magistrates ordered the partial closure of its Taranto plant due to serious health concerns. In November seven top company managers were arrested as part of a corruption probe.