Mercedes' lawyers have labelled Red Bull's actions in Australia as a "flagrant breach" of the rules during Monday's hearing in Paris.
Red Bull Racing are at the FIA's headquarters seeking to have Daniel Ricciardo's Australian GP disqualification overturned.
The Aussie, who finished second on the track, was excluded from the results when his RB10 was found to have "consistently exceeded" the maximum allowed fuel flow rate of 100 kilograms per hour.
Red Bull appealed the ruling and on Monday morning arrived in Paris for the hearing.
According to Associated Press, Red Bull's lawyer Ali Malek gave his argument, stating that the sensors are "obviously unreliable" and that Ricciardo's disqualification was based on a "flawed and incorrect" interpretation of F1 rules.
The Bulls also revealed that while they had initially turned down Ricciardo's fuel flow rate after being told to, they put it back up when the Australian driver lost pace.
However, Mercedes, who are present along with McLaren, Force India, Lotus and Williams, hit back at that.
The Brackley team's lawyer Paul Harris claimed that Red Bull were in a "flagrant breach" of the rules and that they believe they are "entitled to pick and choose between the measurements."
Harris added that the FIA sensors were "rigorously tested and rigorously calibrated" while the sensors Red Bull relide on in Australia were not "100 percent" accurate.
PlanetF1 will bring you more news as it emerges...