The popular fast-food restaurant in Lostock Lane, near B&Q, said it is experiencing "technical issues" and is unable to serve its famous flame-grilled burgers.
Crestfallen customers were informed by staff at lunchtime that all beef products were temporarily off the menu.
A notice posted at the till read: "Due to technical issues we are unable to serve any of our flame grilled beef burgers today, however, we are still able to sell chicken products vegetarian products and fried products.
"Sorry for any inconvenience caused."
It is not clear what type of "technical issue" has affected the restaurant or for how long the beef burgers will be unavailable.
BK Meals removed from today's menu include the famous Whopper (and double Whopper), Smokey Black Angus, Bacon Double XL, Texas BBQ King, Bacon King, Cheeseburger (inc. double) and kids hamburgers.
Staff have apologised to customers and reassured them that the veggie bean burger and chicken options are still available.
One despondent customer, Mark William Doyle, from Preston, said he had nipped into the burger chain with colleagues for a "Friday work treat".
He said: "Treat of the week and we all walk into this! Far from the King of Burgers today!"
Management at the Burger King in Bamber Bridge declined to comment.