Former Labour leader Jeremy Corbyn has been suspended from the party after the human rights watchdog found it broke equality law in its handling of anti-Semitism.
A damning report by the Equality and Human Rights Commission found the party was responsible for unlawful acts of harassment and discrimination.
Mr Corbyn rejected some of the report's findings and claimed the issue had been "dramatically overstated for political reasons" by his critics.
His comments prompted Labour leader Sir Keir Starmer to take decisive action against his predecessor.
Sir Keir told reporters: "If – after all the pain, all the grief, and all the evidence in this report – there are still those who think there's no problem with anti-Semitism in the Labour Party, that it's all exaggerated, or a factional attack, then, frankly, you are part of the problem too.
"And you should be nowhere near the Labour Party either."
Sir Keir said the findings of the EHRC investigation marked a "day of shame" for Labour and he was "truly sorry" for the pain caused.
Mr Corbyn denied he was "part of the problem" and told broadcasters he would not quit Labour: "Of course not. I am proud to be a member of the Labour Party, I joined the Labour party when I was 16, I've fought racism all my life, and I'll fight racism for the rest of my life."
A Labour Party spokesman said: "In light of his comments made today and his failure to retract them subsequently, the Labour Party has suspended Jeremy Corbyn pending investigation.
"He has also had the whip removed from the Parliamentary Labour Party."