Police have threatened action against betting website Paddy Power after they had pilots write a message in the sky over Medinah Country Club.
The message read: "Do it for Seve #GoEurope".
At first, it was unclear who had arranged for the message to be written, but it later transpired that it was Paddy Power who paid for a tweet to be relayed to the European team.
It is part of a gimmick that the betting outpost have during the Ryder Cup, in which they are retweeting messages of support for Jose Maria Olazabal's men, who are playing on American soil.
A post on Paddy Power's Twitter page read: "BREAKING: Feds now threatening our pilots with arrest. Stephen, Maverick, Ice Man & Goose were heroes yesterday! #GoEurope"
USA currently lead Europe 10-6 heading into today's singles matches.