Starting at the Barcelona event, the FIA told teams that numbers and names had to match a set of minimum requirements to make them more visible.

Race numbers should be at least 230mm high and names should be 150mm, both clearly visible on the bodywork.

The FIA stewards said after the race that the number on the cars of Sergio Perez and Esteban Ocon did not comply with the regulations.

The ruling body did not specify what the actual issue was.

"Following a report from the Race Director, Alleged breach of Article 9.2 of the FIA Formula One Sporting Regulations in that the numbers on cars 11 & 32 [sic] do not comply," the stewards said.

Force India enjoyed its best race of the season so far, with Perez finishing in fourth and Ocon in fifth.