The European Court of Justice is expected to deliver judgement in the next few months on a £54m development at a Flintshire cement works. Five judges are considering if EU laws were broken when planning permission was granted for a new kiln at the Castle Cement plant near Mold.
The case was brought against the UK government after environment campaigner Klaus Armstrong-Braun complained. Castle Cement said a full environmental impact assessment had been made.
Mr Armstrong-Braun, a former county councillor, claimed that planning procedures were flawed because a public inquiry into the building of the kiln at the plant at Padeswood did not consider the environmental impact.
The case was heard in Luxembourg last week, and the judges will deliberate before giving a ruling. The kiln is expected to begin burning a new fuel, cemfuel, specially developed for the cement industry.
The company said the fuel, made from recycled office chemicals, would be cleaner and safer. Another special fuel, profuel - made from recycled plastic, paper and cardboard - will be used at Padeswood later this year.
The company said the two new fuels would largely replace the fossil fuels currently used at the plant. Both fuels have been authorised by the Environment Agency.
Castle Cement said it was aware that Mr Armstrong-Braun had referred the matter to the European Court of Justice at the time of the public inquiry, but it had heard nothing further since.
In a statement, the company said: "A full environmental impact assessment was prepared at the time of the planning application in 1999 and all of the environmental aspects were debated at the public inquiry".