The European Court of Justice (ECJ) has given a preliminary ruling on the requirement to comply with an obligation of transparency when making significant changes to a service concession. The case (C91/08) concerned a service concession for the operation and maintenance of public restrooms for the City of Frankfurt. The contract was awarded to a public-private joint venture company, FES, in which the City of Frankfurt held a stake. A competing bidder, Wall AG, was designated under the contract as a sub-contractor. Subsequently, Wall AG was replaced as sub-contractor and took a challenge before the national court, claiming that a substantial change to the contract amounted to a breach of the general principles of EU law. The national court referred a number of questions to the ECJ. On 13 April 2010, the ECJ confirmed that although service concessions are not covered by the public procurement rules they are governed by the obligation of transparency under EU law. The Court went on to state that material amendments to a concession contract can give rise to an obligation to ensure transparency, and this could extend to a requirement to re-tender the contract. The ECJ did not however recommend the national court order the concession be terminated in this instance. It left it to the national court to determine how best to compensate the appellant.