Stars who attended Punk'd star Ashton Kutcher's 30th birthday party in New York are among those being urged to get a vaccination against Hepatitis A.
Ashton Kutcher and Demi Moore were married in 2005
New York health officials are concerned after an employee at the Socialista bar in Manhattan's West Village was diagnosed with the condition.
Madonna, Gwyneth Paltrow and Kutcher's wife Demi Moore were just some of the celebrities who attended the bash.
Anyone who visited the bar on 7, 8 or 11 February should also get the jab.
In a statement, the health department said patrons who visited the bar after the bartender became infected were "considered to be at risk and needs a preventive shot".
It said the bar owners were co-operating fully and estimated between 700 and 800 people had visited the bar on those nights.
No cases of illness had yet been identified, it added.
Other stars pictured at Kutcher's party included Ivanka Trump, Liv Tyler, Catherine Keener, Lucy Liu and Salma Hayek.
Also reported to have attended were Javier Bardem, who is up for a best supporting actor Oscar this weekend, and fashion designer Roberto Cavalli.
Hepatitis A is a viral infection of the liver which leads to weakness, lack of appetite, abdominal pain, nausea and jaundice.
Up to 10 million people are affected by the condition worldwide every year.