It may sound like an episode of Punk'd – but this time it's real.

Guests at Ashton Kutcher's 30th birthday party at the trendy New York bar Socialista are being urged to get a Hepatitis A vaccination because one of the bartenders was infected.

Among the A-listers at the Feb. 7 event: Kutcher's wife Demi Moore, Madonna, Bruce Willis, Gwyneth Paltrow, and Salma Hayek.

The bartender also worked on Feb. 8 and Feb. 11.

"We are asking these bar patrons to get this vaccination as a precautionary measure," said Dr. Sharon Balter, medical epidemiologist at the New York City Department of Health and Mental Hygiene.