Fast-food giant MOS Burger has come under fire after a Japanese employee wrote a hateful message about a former Chinese co-worker on a chalk-board sign outside one of the company's Tokyo restaurants.

A photo dated Tuesday that went viral on Twitter shows the message, which states: "I told my unpunctual Chinese colleague that I will make ramen out of her back fat if she comes in late one more time. (After that), she stopped being late."

The chalkboard was located outside a MOS Burger outlet in Tokyo's Iidabashi-higashi district, the company confirmed.