ULSTER GAA chiefs are facing a legal challenge over the planned £70 million redevelopment of Casement Park stadium, it emerged yesterday.Two construction companies whose combined bid to win the contract was unsuccessful have launched High Court proceedings in attempt to get back into the tendering process.Papers were lodged on behalf of Lagan Somague, a joint venture involving firms from Northern Ireland and Portugal.A new stadium is due to be built on the existing Casement site in west Belfast at a cost expected to top £70m.Most of the funding is coming from the executive through the Department of Culture, Arts and Leisure.The redevelopment forms part of an overall £110m investment plan involving upgrades to the Ulster rugby ground at Ravenhill and Windsor Park football stadium.A legal challenge by soccer club Crusaders to the Windsor Park proposals is ongoing. Now, however, proceedings have been brought against the GAA's Ulster Council.The case is expected to centre on its duty as a contracting authority under European procurement regulations. Lawyers for Lagan Somague are expected to argue that they have been wrongly knocked out of the tendering process.An initial hearing is expected to take place in court next week.