After intense discussions between rival outfits and the FIA on the race morning of the Monaco GP, Red Bull team principal Christian Horner confirmed that a formal protest against the team has been lodged by the world champion squad.
Furthermore, AUTOSPORT can reveal that Ferrari has also written to the FIA demanding clarification about the testing restrictions in light of Mercedes using a 2013 car.
Mercedes conducted 1000km of running over three days at Barcelona in the week following the Spanish Grand Prix at the request of Pirelli.
Article 22 of the F1 sporting regulations outlaws any form of in-season testing at F1 venues except for a young driver test and straightline aerodynamic running. The only other way an F1 team can run is with a 2010 car.
Although Mercedes insists that Pirelli's contract with the F1 squads allows it to call upon teams to conduct private tests when it is required, rival outfits are adamant that this cannot supersede the sporting regulations so cannot be with a 2013 car.
In addition, while other teams have also conducted similar tests in the past, these have always been done in line with the regulations.
Ferrari conducted a tyre test for Pirelli at Barcelona after the Bahrain Grand Prix, but it was done with a 2010 car to avoid falling foul of the F1 rules.
Both Ferrari and Red Bull are adamant that the use of a 2013 car - as Mercedes used - is not allowed.
The matter is expected to be debated by the FIA race stewards after the Monaco GP.