The issue of "burning rubber" is again overshadowing the Formula One season with Mercedes facing an official investigation over whether the team carried out an illegal tire test.
The sport's ruling body -- the FIA -- launched the probe after rival teams Red Bull and Ferrari lodged an official protest at the weekend's Monaco Grand Prix after discovering sole tire supplier Pirelli and Mercedes had carried out a three-day development test.
In May, Pirelli asked the FIA if it could carry out testing with an F1 team. The sport's rules state that 1,000 kilometers of testing with any marque is allowed during the season -- as long as every team is offered that opportunity.
"Pirelli and Mercedes-AMG were advised by the FIA that such a development test could be possible if carried out by Pirelli, as opposed to the team that would provide the car and driver, and that such tests would be conditional upon every team being given the same opportunity to test in order to ensure full sporting equity," said an FIA statement.
However, the FIA says it did not hear back from Pirelli or Mercedes and received no confirmation all the teams had been been given the chance to take part.
Monaco Grand Prix stewards will now write a report to the FIA regarding the Pirelli and Mercedes test.
"It should be remembered that the International Sporting Code provides that on the basis of a report of the stewards of the meeting, or on its own initiative, the prosecuting body of the FIA may bring a matter before the International Tribunal," added the FIA statement.
"The Tribunal may decide to inflict penalties that would supercede any penalty the stewards of the meeting may have issued. Such procedure would be followed in pursuance of the FIA judicial and disciplinary Rules."
Pirelli insists it has done nothing wrong in organizing the test.
"All teams were invited to carry out this kind of test, in accordance and with the full agreement of FIA," said Pirelli in a statement.
"Someone replied positively, someone else showed no interest. Whoever will want to do a test with us is welcome. "
Mercedes was not immediately available for comment.
During this season, particularly after the Spanish GP earlier in May, many involved at the top end of the sport have argued tire degradation was ruining F1 racing given the number of pit-stops being made.
After that stop-start Spanish Grand Prix, Pirelli subsequently admitted that some of the testing it had conducted on their tires had been had not been ideal.
"Winter tests are inadequate and carried out in conditions far from the reality of the season's races," a Pirelli spokesman told CNN. "The cars are much faster this year than last year (as well)."