Mercedes are said to be at the centre of a row in Formula 1 because of tyre testing that took place between the Spanish Grand Prix and this weekend's Monaco Grand Prix.
According to BBC Sport, the German team had a three-day test with some new Pirelli tyres that could be introduced to the sport at the next Grand Prix in Canada.
In-season testing in F1 is forbidden and Red Bull and Ferrari could protest against Mercedes, who have both cars on the front row at this afternoon's race in Monte Carlo.
The plans to introduce new tyres, which reduce rear wheel delamination, in Canada are yet to be approved by Ferrari, Lotus and Force India.
