Lewis Hamilton says one team is stalling on signing his diversity charter for Formula 1 and has called on the sport to "do more".
The charter, proposed by a commission set up by Hamilton, aims to encourage more diversity and help those from under-represented backgrounds enter F1.
But Hamilton said on Thursday at the French GP: "We are very close to getting this diversity inclusion charter going and I think it's still one team, still the same team, is not willing to engage.
"We've gone back and forth to them and for some reason they don't want to, but all the other nine teams have which is really encouraging."
Hamilton refused to name the team, though Sky Sports has learned it is Williams. In response, the team said: "We last had conversations with the Royal Academy of Engineering back in March and we are awaiting further information from them on such an important topic, of which we at Williams Racing already have serious active programmes.
"We have no knowledge of the progress and of who has and has not signed up to date, as it has been several months since we had any communication from them.
"Once we are in possession of further information and a copy of the final charter, we can look into it."
The Grove team have their own employee-led diversity and inclusion programme.
"F1 needs to do more," added Hamilton ahead of the French GP, as he also called for more action after fans were subjected to racist, sexist and homophobic abuse at the last race in Austria.
"I'm doing the most I can, I don't know what else I can do," he said. "I think it's all of our responsibility to do something."
Sergio Perez said on fans involved in offences: "We definitely should ban them for life. Don't welcome them again, because they don't represent who we are as a sport, and they don't share our values at all.
"But at the same time we have great fans out there and with great values and I think a few fans shouldn't be able to even embarrass our sport like that."