Keir Starmer is to remove the whip from MPs for persistent rebellions, starting with at least four of them on Wednesday afternoon.
The Guardian understands that four MPs set to lose the whip are Rachael Maskell, Neil Duncan-Jordan, Brian Leishman, and Chris Hinchliff.
One Labour source said the whip was being removed from “persistent rebels”.
All four MPs facing suspension have been openly critical of several government policies, including the welfare bill and cuts to the winter fuel allowance.
MPs who lose the whip are no longer considered part of the parliamentary party, though they retain party membership unless that too is revoked. The suspension is usually for a set period, and then reviewed.
Leishman said in a statement: “I am a proud Labour member, and I remain committed to the party. I wish to remain a Labour MP and deliver the positive change many voters are craving.
“I have voted against the government on issues because I want to effectively represent and be the voice for communities across Alloa and Grangemouth. I firmly believe that it is not my duty as an MP to make people poorer, especially those that have suffered because of austerity and its dire consequences.”
Leishman is a member of the leftwing Socialist Campaign Group. Duncan-Jordan and Hinchliff were both elected with very slim majorities in constituencies that have never before returned Labour MPs.
Duncan Jordan said: “Since being elected I have consistently spoken up for my constituents on a range of issues, including most recently on cuts to disability benefits. I understood this could come at a cost, but I couldn’t support making disabled people poorer.
Although I’ve been suspended from the parliamentary Labour party today, I’ve been part of the Labour and trade union movement for 40 years and remain as committed as ever to its values. To my constituents: it’s business as usual.”
It will be the second time Starmer has enforced severe discipline on MPs who vote against the government, after removing the whip from seven MPs who voted with the Scottish National party to remove the two-child benefit cap in the king’s speech last summer.
Those suspended from the whip last July included John McDonnell, Richard Burgon, Ian Byrne, Rebecca Long-Bailey, Imran Hussain, Apsana Begum and Zarah Sultana.
The whip has since been restored to most of those MPs, though several on the left have continued to vote against the government on a number of issues including welfare, the proscription of Palestine Action and on changes to planning.
Sultana, who has remained suspended, announced she was quitting Labour to found a new party with the former Labour leader Jeremy Corbyn, who was elected as an independent in the last election.