Senior leftwing Labour figures have used their new dominance on the party’s governing body to immediately replace the longstanding chair of a key panel that considers disciplinary matters.

The vote to remove Ann Black from her role on the disputes panel and replace her with Christine Shawcroft came a day after the balance of power on the national executive committee shifted further in Jeremy Corbyn’s favour.

NEC members backed Shawcroft, who is a director of the grassroots campaign group Momentum, by 22 to 15, in a move that led to internal clashes between figures on different wings of the party.

One source claimed the leadership team had become frustrated by Black after she voted to make it harder for new Corbyn supporters to vote in his second leadership election.

But another figure on the NEC said they believed the motivation for Tuesday’s vote had been to limit the number of Labour members kicked out of the party for antisemitic behaviour.

The disputes panelmakes decisions about membership appeals and whether to readmit figures who have been removed from Labour in the past.

Shawcroft said the position of chair was up for selection annually.

“This is a storm in a tea cup,” she said. “Every year we have elections for chair of committees. Ann did good work when she was chair and we will both continue to represent the members who voted for us to the best of our abilities.”

But Stephanie Lloyd, the deputy director of the centrist Labour group Progress, said: “Targeting Ann Black shows the contempt the Momentum-left have for party democracy when things do not go their way. Inevitably the hard left turn in on themselves and it is pretty unedifying to watch.”

Critics claimed that deselecting Black had been the first act of the Momentum founder, Jon Lansman, after he and other leftwing candidates were elected to the NEC on Monday.

Supporters of Shawcroft, including the NEC member Rhea Wolfson, were forced to respond to accusations within minutes of the vote that she had recommended referrals of alleged antisemitism for further investigation be overturned.

Rhea Wolfson (@rheawolfson) No she hasn't and people leaking this shit to the media should be ashamed for undermining hard work being done in the party to tackle anti-semitism. https://t.co/AvmmbtSx63

Another source said: “There were debates on some cases about whether to refer for training or whether to send straight to the NCC, but votes were taken on these and the majority view prevailed. Christine didn’t vote on any of them.”

Some believe the party is using claims of antisemitism to purge supporters of Corbyn, but others warned against any move that might weaken Labour’s determination to stamp out such prejudice.

Jennifer Gerber, the director of Labour Friends of Israel, said: “The hard left have spent two years denying Labour has a problem with antisemitism. They must not now be allowed to stifle investigations into it or action to combat it.”