Italian Grand Prix race winner Lewis Hamilton and Nico Rosberg are under investigation by the FIA race stewards for a potential breach of the minimum tyre pressure regulations.
Following guidelines issued by tyre supplier Pirelli, teams were supposed to be above the 19.5 PSI at the start of the race.
However, an investigation by the FIA showed that Hamilton's left hand side rear tyre was 0.3 PSI below that mark, with Rosberg's 1.1 PSI under.
The notification to the team was sent at 15:04, which explains why Hamilton was asked to push as hard as possible over the final laps of the race.
The matter is being referred to the stewards and any punishment could cost Hamilton his victory.
Mercedes technical chief Paddy Lowe 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.
“I’d call it an abundance of caution, because we haven’t done anything wrong. We thought ‘let’s make a gap’.
"We've been summoned to the stewards so we'll go there and explain it."