Formula One's governing body accused the Mercedes team on Thursday (June 20) of breaking the rules by testing in Spain with tyre supplier Pirelli last month and benefiting from their involvement.
Mercedes, the team of 2008 world champion Lewis Hamilton and Germany's Nico Rosberg, could face heavy sanctions if found guilty by a tribunal meeting at the International Automobile Federation (FIA) headquarters.
Mark Howard, the FIA's legal representative, opened the hearing by telling the four judges and tribunal president Edwin Glasgow that there was little factual dispute in the case presented to them.
Mercedes have said they tested at the Barcelona circuit after the Spanish Grand Prix with their 2013 car, but have stated that the test was organised by Pirelli - who are not competitors - and they gained no advantage from it as a team.
They have also said they acted in good faith and believed they had secured the approval of the FIA.
Howard said their action was a clear breach of the ban on teams testing during the season with a current car and that the team would have gained valuable information from the test, even if only to highlight some previously unknown defect with the car.
Mercedes, who had principal Ross Brawn attending the hearing along with chief race engineer Andrew Shovlin, sporting director Ron Meadows and lawyers, was expected to be heard later before Pirelli also present their views.
Presented by Adam Justice