"Team orders designed to influence the outcome of a race are not permitted."
This is clearly stated in Article 39.1 of the FIA regulations, the ruling introduced after Ferrari manipulated the race result two years in succession at the Austrian GP in Spielberg. In 2002, Jean Todt famously told Rubens Barrichello over the radio: "Let Michael pass for the championship."
Eight years later, another Ferrari radio message goes into the motorsport history books. This time, it was Felipe Massa's race engineer, Rob Smedley, who had the job of breaking the news to the Brazilian: "Fernando is faster than you. Can you confirm that you have understood that message?"