Brackley-based Mercedes are at an FIA tribunal in connection with their controversial Pirelli tyre test.
Mercedes' defence rests heavily on their assertion that they were given permission by FIA race director Charlie Whiting to use their current 2013 car at the test.
However, Mark Howard QC, speaking first on behalf of the FIA as the body's legal representative, said Whiting's consent was "irrelevant".
Howard said that Whiting was not authorised to amend Article 22 of the sporting regulations - which covers the ban on in-season testing - saying such a move could only be undertaken by the FIA's World Motor Sport Council.
The FIA's hearing into last month's contentious Mercedes and Pirelli tyre test got under way in Paris this morning.
The Brackley-based F1 outfit are appearing at the tribunal after they appeared to contravene the FIA's ban on in-season testing by their current car and regular drivers in a three-day, 1,000-kilometre test held in conjunction with Pirelli in May.
Team principal Ross Brawn was a witness for the Mercedes delegation, with Pirelli motorsport director Paul Hembery appearing for the Italian tyre manufacturer.
Legal representatives of Ferrari, McLaren and Williams were also in attendance, as was Red Bull team principal Christian Horner.
Lewis Hamilton's first day behind the wheel of his Mercedes F1 car built at Brackley in Northamptonshire resulted in a crash into a tyre barrier. It was on the second day of testing at the Spanish Circuito de Jerez this morning.
The 28-year-old from Stevenage locked up into turn six and ploughed through a gravel trap into the tyre barrier. It's thought a fault in the front suspension caused the crash.
Yesterday Hamilton's team mate Nico Rosberg ground to a halt after just 14 laps when an electrical fault led to a fire in the rear of the new Mercedes.
Mercedes have launched their new formula one car at Jerez in Spain. It's the last of the three fomula one teams based in our region to reveal its new car. The Mercedes will be driven by Lewis Hamilton this season after he signed from McLaren.
Mercedes, based at Brackley, in Northamptonshire, had a disappointing season last year despite scoring their first win with Nico Rosberg, who will partnering Hamilton this season.