Speaking before the FIA confirmed that both Mercedes and Pirelli have been charged to appear before an International Tribunal hearing on June 20, Red Bull boss Christian Horner made it clear that the key issue for his team was that its Brackley-based rivals had run a 2013 car.
That is why his outfit, along with Ferrari, elected to lodge an official protest against Mercedes in the hours leading up to the Monaco Grand Prix.
"I think the issue is nothing to do with Pirelli," he explained. "I can understand fully why Pirelli would want to test.
"I think they wanted to understand the product for the following year.
"The issue was they asked for a car to be used, and it is the entrants' responsibility to ensure that that car complies with the rules.
"Our issue is not to do with Pirelli; it is to do with the current entrant. They [Mercedes] broke the rules with the current car."
Pirelli organised the test at Barcelona as part of some early preparation work for 2014.
The tyre company had simply requested a 'representative' car from Mercedes, while the team claims it got permission from the FIA to run an actual 2013 model.
Horner, whose team has been openly critical of the tyres this year, reckoned that it made complete sense for Pirelli to get some valuable testing mileage.
"Absolutely - but only if that was done with unanimous agreement of all the teams, or all the teams carried out a test," he added.
"What you cannot have is a test for one team because, of course, you are learning at that test, whether it be for reliability, whether it be driver seat time, whether it be other components that the team may or may not have had on the car.
"In our view the test contravenes the regulations."
Horner did suggest, however, that Pirelli could have handled the communication of the test better.
Rival teams only founds out that Mercedes had tested when news of the run emerged during a meeting of the Grand Prix Drivers' Association (GPDA).
"It is disappointing to learn second hand that Mercedes has done a three day test and then it transpires Ferrari has done one in a two-year-old one as well," Horner said.
"All that kind of stuff should be above board and transparent."