Lewis Hamilton and Mercedes have been summoned to the stewards' office following his Italian Grand Prix victory.
Reigning World Champion Hamilton won Sunday's race at Monza from pole position, finishing 25s ahead of Ferrari's Sebastian Vettel with Felipe Massa of Williams third.
However, the Mercedes driver has been ordered to appear before the stewards to explain the tyre pressures as it were below Pirelli's minimum.
Hamilton had a 20s lead over Vettel with about five laps to go before the team told him to push hard and "they would explain at the end of the race". He obliged and finished 25s ahead while Rosberg retired a few laps before the end.
The rear left tyre was reportedly 0.3psi below the limit while Rosberg's was 1.1psi below, but Mercedes motorsport boss Toto Wolff told BBC Sport: "No because we measure them with Pirelli. At the moment we have no detail what is going on."
He added: "We are the first to be sure (we are safe and legal)."
Meanwhile Paddy Lowe, Merc's technical chief, insists Mercedes did everything they were supposed to do.
He said: "We don't understand it, to be honest.
"All I know is we set our pressures fully supervised by the Pirelli engineer, he was perfectly happy with them, as they were set. We'll go and investigate.
"We've been summoned to the stewards so we'll go there and explain it."