It comes for an “Alleged breach of Article 2.5.1 of the FIA International Sporting Code.”
That article relates to the sanctity of parc ferme.
“Inside the parc ferme, only the officials assigned may enter,” Article 2.5.1 of the FIA International Sporting Code states.
“No operation, checking, tuning or repair is allowed unless authorised by the same officials or by the applicable regulations.”
That issue, which specifically related to the DRS system on Hamilton's car, was found during post-qualifying scrutineering.
Some suggested it was a result of a complaint from Red Bull, though the team has denied that claim to Speedcafe.com.