Mercedes has argued that its running of a 2013 car during the post-Spanish Grand Prix test at Barcelona was not a breach of the regulations.
After hearing the submissions of the FIA to the International Tribunal judges, Mercedes lawyer Paul Harris QC argued that the Brackley-based outfit did not break the rules because the track run was a Pirelli test.
The FIA believes that Mercedes may have breached Article 22 of the Sporting Regulations by running its current contender.
The rules state explicitly that testing is classified as "any track running time not part of an Event undertaken by a competitor entered in the Championship."
Harris says that the fact the test was organised, paid for and run by Pirelli means that Mercedes cannot be ruled to be in breach.
"This was not a test undertaken by Mercedes. They are critical words in text of Article 22 - 'undertaken by'," he said.
He added: "The Pirelli test was not a test undertaken by Mercedes, it is irrefutable it is a test undertaken by Pirelli."
Harris said that Pirelli directed, controlled and paid for the test, and that Mercedes was only doing what it was requested to by the Italian tyre manufacturer.
"This evidence is confirmed by Pirelli, so the people who were present on the day all unanimously give the same evidence about what was going on, who was doing it, and who was in charge of it. It is undeniable the testing was undertaken by Pirelli."
Harris said that Mercedes team principal Ross Brawn and team manager Ron Meadows did have permission from F1 race director Charlie Whiting and FIA lawyer Sebastien Bernard that it was allowed to run its 2013 car at the test.
Mercedes claims that its view that the test was being 'undertaken' by Pirelli and not Mercedes was backed in correspondence between Whiting and Bernard.
In an email on May 3 that Whiting wrote to Bernard, Harris quoted the F1 race director as saying: "In my view any such testing would not actually be undertaken by the competitors, it could be be argued that this was done by Pirelli. Would we be able to take this position?"
Bernard replied: "Indeed we could take this position...[it is] not an undertaking from the competitor."