Hamilton, the six-time Formula 1 champion who won the 90th race of his career on Sunday, wore a T-shirt with the words “Stop the Killers of Briona Taylor” and “Say Her Name” over a photo of Taylor on his back before the race and at the coronation ceremony.
“The situation is under active study for an explanation that will be in place for the next race,” an FIA spokesperson told CNN.
The spokesperson did not confirm which rule Hamilton will be investigated for breaching.
Taylor was killed by a fatal bullet at her home in Louisville in March when three plainclothes police officers executed a “do not hit” warrant.
“It’s been six months since Briona Taylor was killed by police officers in her home,” Hamilton wrote on Twitter alongside photos of himself wearing the shirt. “So far, justice has not been served. We will not remain silent.”
He also added at the post-race conference: “It took a long time to get this shirt and I wanted to wear it and spread awareness of the fact that there were people killed in the street and another person was killed in her house.”
“We have to keep raising awareness … I think we just have to keep pressing on this issue.”
A Tuscan GP win means Hamilton is now one distance away from tying up Michael Schumacher’s record of 91 Formula 1 wins.
He also announced plans to create a committee in his name to increase diversity in motorsport.
CNN’s Elizabeth Joseph and Susanna Cullinan contributed to this report.