Sheffield City Council is at risk of falling apart after the Labour Party ordered its local branches to end any power-sharing arrangements with the Greens, unless local councillors disavowed the controversial Zionism is racism motion.
In the Steel City, the council is governed in coalition between the two parties, with Labour with 26 councillors and the Greens with 19.
However, after the motion voted through at the Green Party conference, which Prime Minister Andy Burnham has described as anti-semitic, the Labour Party could pull out.
Chair Bridget Phillipson has written to all Labour council groups who are currently in coalition, or other power-sharing arrangements, with the Greens, asking them to write to the party and seek “reassurances” that they condemn the motion.
If the Greens do not respond in seven days, then Labour has said it will end its power-sharing arrangements.
This will impact 17 councils across England and Wales, although Sheffield is the only local authority in Yorkshire affected.
Sheffield Labour has been contacted for comment by The Yorkshire Post.
Writing to the councils, Ms Phillipson said: “Where local Labour parties currently have an arrangement with the Greens in local government, we expect their Green counterparts to make clear that they reject this position and to call on their national leadership to reconsider the policy.
“We have asked local Green groups to respond as a matter of urgency.
“Where they are unable to provide that assurance, Labour will bring any such local arrangement to an end.
“This isn’t an issue of party politics; it’s about doing what is right and upholding the values anyone holding public office should share.
“The Labour Party fought hard to address antisemitism within our own party and ensure it had no place in our politics.
“We have a responsibility to uphold those same standards in our relationships with other parties.”
This comes after Prime Minister Andy Burnham ruled out any coalition with the Green Party on a national level in future, while the policy is in place.
Asked about the Zionism is racism motion at Prime Minister’s Questions, Mr Burnham said he condemned it “unequivocally” and would not support a “partnership” with the Greens while it remained in place.
The Labour Party leader said: “It is wrong, it is antisemitic, and this side of the House will have nothing to do with it.
“We will always take the right response when it comes to any partnerships we have with other parties.
“We cannot support a partnership with a party that holds the position that has recently been adopted.”
Green Party leader Zack Polanski, who did not vote on the motion, has attempted to distance himself from it, saying he would only have supported it if it was amended.
The motion effectively makes the belief in a Jewish homeland - Zionism - regarded as any other form of racism.
He told Sky News: “Ultimately, I agree with the substance of the motion. Where I disagree is the idea the Green Party should be deciding what the future of the region looks like.”
It has been a bruising few weeks for Mr Polanski, who lost the Holborn and St Pancras by-election.