Celebrity hotspot and renowned Japanese restaurant Nobu has written a note to diners at its London restaurants warning them not to eat the bluefin tuna on the menu because it is endangered, the London Telegraph reported Wednesday.

The restaurant, popular with stars like Brad Pitt and Kate Moss, calls the $50 dish on its own menu "environmentally challenged." It asks patrons to "ask your server for an alternative."

Animal activists have long campaigned against Nobu for continuing to serve the bluefin, which is on the brink of extinction. An undercover Greenpeace investigation claimed waiters at Nobu said the tuna was not bluefin, when DNA tests proved the threatened fish was being served, the Telegraph reports.

Restaurateur Tom Aikens told the Telegraph that the bluefin was probably one of Nobu's best-selling dishes, and its removal from the menu would hurt the restaurant financially. He called the new menu warning "very peculiar."

Giles Bartlett, senior policy officer for WWF, told a British paper that bluefin shouldn't be on Nobu's menu at all.

"They shouldn't sell endangered species," he said. "They should change their menu to incorporate a fish that's sustainable and not one that's critically endangered."

Click here to read more on this story from the Telegraph.