Chelsea chairman Bruce Buck says the club will not tolerate what he deemed as abuse bordering on racism directed by fans at manager Avram Grant.
Israeli Grant, 52, has succeeded Jose Mourinho as Chelsea boss and his side drew 0-0 with Fulham on Saturday.
"We welcome constructive points of view but we've had a few which could be seen as racist and anti-Semitic," said Buck.
"This is one thing we will not tolerate whether written, on banners, or through singing and it must stop immediately."
Grant's Polish father Meir, 80, is a Holocaust survivor and Buck continued: "It unfairly smears the reputation of the vast majority of the Chelsea fans who rightly do not want to be associated with such activity."
Chelsea supporters were also chanting the name of Mourinho during the second half of their game with west London rivals Fulham at Stamford Bridge.
And the club's billionaire owner Roman Abramovich, who sat with fans in the upper tier of the Shed stand instead of his private box, was forced to endure their taunts.
