Mercedes was warned last year that there was no scope in the Formula 1 regulations for any private in-season testing.
As the Brackley-based team awaits news from the FIA about whether or not its recent Pirelli tyre test is to be investigated further, it has emerged that an email clarifying the testing situation was sent in April last year.
Addressed to all the teams, the FIA and Pirelli and written by the Formula One Teams' Association (FOTA), the email makes it clear that a tyre test can only take place if there is unanimous support among the teams.
The email, a copy of which has been seen by AUTOSPORT, states that following discussions with the FIA, it is clear that in-season tyre testing for Pirelli by a single team cannot take place.
"Pirelli is entitled under the terms of their agreement with the FIA to offer teams 1000km of tyre testing, subject to each team being treated equally," said the email.
"However there are no provisions within the Sporting Regulations for such testing to take place in-season.
"[FOTA has] spoken with Charlie [Whiting] to confirm the process going forward, and there are two options: 1. ALL teams want to take up Pirelli's offer and this is communicated to the FIA who will amend the Sporting Regulations; or 2. The test takes place out of season (and then the testing agreement comes into play)."
One month before the FOTA clarification, Pirelli wrote to the teams explaining that there was the possibility for 1000km of testing.
It was in this letter, sent by Pirelli to the teams, Bernie Ecclestone and the FIA, that the initial offer for teams to take part in such a test was made.
"Within our agreement with the FIA there is a provision to invite all teams to perform 1000km of tyre testing," wrote Pirelli motorsport chief Paul Hembery.
"If this is something your team would be interested in pursuing, please advise your interest so an eventual test date could be set. We would provide the track and service support."
Mercedes is adamant that it had more recent authority from the FIA to run its 2013 car at the Barcelona test, which took place in the week after the Spanish Grand Prix.
However, a statement issued by the FIA on Sunday night suggested that its approval for the test was conditional on all teams being invited to take part, and the car being run by Pirelli rather than Mercedes.
Following a protest by Red Bull and Ferrari over the matter, the Monaco GP race stewards are preparing a report for the FIA to judge whether or not the matter warrants a hearing.