The Labour leadership needs to take a "much clearer and firmer line" on anti-Semitism, Christians on the Left has said.
The campaign group said the Labour Party needed to be "firmer at all levels" in addressing anti-Semitism and that it no longer had confidence in the Party's internal disciplinary processes.
The statement comes in the same week as the Labour leadership was forced to turn back on its decision to reinstate MP Chris Williamson, who had been suspended in a row over anti-Semitism.
Following a backlash, the Labour Party announced that he would remain suspended.
The U-turn followed an open letter signed by 90 Labour MPs and peers condemning the decision to lift the suspension of Mr Williamson.
Even before the last week's events, Labour leader Jeremy Corbyn has struggled to convince critics that he is taking complaints of anti-Semitism in the Party seriously.
In a statement, Christians on the Left said that "anti-Semitic and racist views and behaviour are unacceptable and have no place in the Labour movement".
"We believe that there needs to be a much clearer and firmer line from the leadership of the Party that anti-Semitism will not be tolerated, ignored, or excused," it said.
"We believe the Labour Party needs to be more positive about its values and what they mean in practice, and firmer at all levels in dealing with anti-Semitism. We no longer have confidence that existing internal disciplinary processes are fit for purpose."
The group called on the Party leadership "to challenge and remove" all instances of anti-Semitism and racism within the membership, and introduce "transparent" disciplinary procedures enacted by an independent disciplinary body.
"We have been a proud affiliate of the Labour Party over many years and Labour values are central to our organisation," the statement concluded.
"We share the spirit of solidarity, tolerance and respect which has always defined our party and believe that it is imperative that this continues to be the case."
