Two Coventry city councillors have resigned from the Labour group after claiming they have been bullied and harassed by colleagues.
Valerie Stone and Kate Hunter, who represent Longford and Radford respectively, say they will now become independent councillors.
They say their health and family life have been affected.
Labour says it is extraordinary they have resigned before an independent report about the group is published.
It has now called on them to resign their seats.
Their decision means that Labour has 20 city council seats, seven fewer than the ruling Conservative group.
The pair claim they have suffered "intolerable treatment" and "a catalogue of unpleasantness" including verbal abuse, intimidation and victimisation.
Kate Hunter said: "It's this general whispering campaign, this trying to undermine your credibility.
"All they have to do is label you as a troublemaker and say it often enough and sometimes people don't challenge (them by saying) 'why are you saying they're a troublemaker'.
"In a society where we're trying to make the council more representative, to lose four women in the space of two years is quite incredible."
John McNicholas, the Labour group's secretary, said: "It is true that there is an ongoing independent investigation into matters pertaining to the Coventry Labour Group.
"The two councillors in question were due to be interviewed at that inquiry. But to resign before that inquiry has given its report is extraordinary.
"Local people voted for Labour councillors not independents.
"If they want to serve as independent councillors then they should go back to the electorate and ask them if that is what they want."