It has emerged that Mercedes conducted a private three day tyre test following the Spanish Grand Prix.
Autosport and BBC Sport claim ahead of the Monaco Grand Prix that the Brackley based team carried out over 1000 kilometres of running.
It is understood the tyres tested were the modified tyres, which will be introduced at next month's Canadian Grand Prix. Also tested were prototype 2014 tyres, should Pirelli continue in the sport.
Pirelli claims they are permitted to call on a team should the situation arise. Rival teams are unhappy that the test was not carried out in a transparent manner.
"I think there’s confusion between what is contractually permissible and what isn’t, and what a team when it enters the World Championship is allowed to do within the sporting regs. It’s a situation that we need clarification on, and our position is that we are going to request that clarification," Red Bull team principal Christian Horner told Autosport.
"I can understand Pirelli wanting to test the tyres – they’ve obviously got issues with the tyres. What’s disappointing is that it’s been done in not a transparent manner. A three-day test has taken place running a current car on tyres that are going to be used in the next Grand Prix. Irrelevant what you call it, that’s testing."
