Carl Sunley, a sous chef at Ricci's Tapas and Chicchetti at Goodbard House, Infirmary Street, said his key for the premises did not work when he tried to open up this morning.
Around 18 to 20 people are employed at the restaurant, he said.
The 27-year-old said: "I turned up to work this morning and the locks has been changed and lights were off.
"We had an extremely busy Christmas. We were turning over tens of thousands in December."
Mr Sunley, who says he has rent to pay, added: "I'm going to have to reach out to friends and contacts and find a new job very quickly."
The business also has a site at the Dean Clough mills complex in Halifax.
Ricci's was awarded in the Best World category of the YEP's Oliver Awards last March.
The restaurant's owner has been contacted but did not want to comment.