Members of the Labour Party who helped independent MP Peter Law in his Blaenau Gwent election campaign are expecting to be expelled from the party.
Mr Law has become Wales' second-ever independent MP
Blaenau Gwent Labour Secretary Steve Osborne told BBC Wales he understands letters of expulsion are being sent from party headquarters in Cardiff.
Mr Law, who left Labour over all-women shortlists, defeated the party in what was its safest Welsh seat.
The Welsh Labour Party said 20 members in Blaenau Gwent faced expulsion.
Speaking about the expulsions, Mr Law said the Labour would "bring the roof in on itself" through penalising people instead of expressing regret after losing Labour's safest seat in Wales.
"They are trying to intimidate people who simply stood up for the socialist values people in Blaenau Gwent believe in," he added.
Mr Law, who is also Blaenau Gwent's Welsh Assembly Member, left Labour before the general election over the party leadership's decision to adopt an all-women shortlist to replace retiring MP Llew Smith.
Mr Law withdrew from the electoral contest when he discovered he had a brain tumour, but underwent surgery and decided to press ahead as an independent.
Peter Law defeated Labour's Maggie Jones in Blaenau Gwent
He overturned a 19,000 majority, defeating Labour candidate Maggie Jones by 9,000 votes, to become Wales' second-ever independent MP.
Mr Law said shortly after the election that he might consider rejoining Labour if there was an "amnesty" for party members who backed him.
Last week Secretary of State for Wales Peter Hain told BBC Wales there was no "witch hunt" against Mr Law or "vendetta" against his supporters in Blaenau Gwent.
But the Labour Party has moved to expel those who backed Mr Law's campaign. Grounds for expulsion from the party are believed to include actions such as signing Mr Law's nomination papers.
The Wales Labour Party said on Thursday that 20 members in Blaenau Gwent appeared to have acted in ways which lead to automatic expulsion.
A spokeswoman added that the constituency Labour Party had been advised that unless the members concerned dispute the facts, they should not be allowed to take part in meetings of the party.
She said the expulsion letters are expected to be sent shortly by Labour's ruling National Executive Committee.
The former Labour Blaenau Gwent MP, Llew Smith, told BBC Wales: "Its a disgrace. The people who inflicted this policy on Blaenau Gwent should be punished, not the people who had the courage to stand up and make their voices heard.
"It is a crazy witch hunt by the party in Cardiff."