From a New York Times article about Clinton campaign fundraisers in London organized by Anna Wintour:
The designers Alber Elbaz, Christopher Bailey of Burberry and Tom Ford were among the couple of hundred guests paying $500 each for the gallery event ($1,000 including a photo with Chelsea Clinton) or $2,700 for the dinner. Mr. Elbaz, who cannot vote as he is not an American citizen, said he went to support his partner, Alex Koo, who is. Mr. Bailey, who is British, is a friend of Chelsea Clinton.
From the Federal Election Commission website: "Foreign nationals are prohibited from making any contributions or expenditures in connection with any election in the U.S. Please note, however, that "green card" holders (i.e., individuals lawfully admitted for permanent residence in the U.S.) are not considered foreign nationals and, as a result, may contribute."
It seems like a ripe topic for further press examination given the Clinton past history with questionable campaign cash.