Michael Marra has described Reform UK as "a gateway to something much darker," warning that the party poses an "incredibly dangerous" threat to the country.
The Scottish Labour leadership candidate made the remark as he launched his campaign in Glasgow on Monday.
Asked whether he would ditch Anas Sarwar's "no pacts, no deals, no coalitions" policy and allow Labour councillors to form administrations with other parties after next year's local elections, the MSP said he would — "but not Reform".
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Mr Marra said next May's vote would be very different to 2022's as it would see "six-party politics being projected into four or three-member wards".
"That makes it very difficult, I think, for all of the traditional main parties. Things are going to become more fractured.
"We have to be able to make sure that we can do deals to deliver the best possible for the people of Scotland and the communities we seek to serve.
"So we have to work with local authorities to make that happen, but not Reform.
"Absolutely clear that we can't. I think that the Reform side of this is incredibly dangerous for the country. They are a gateway to something much darker.
"Now there are people who may have voted Labour in the past who voted Reform in May, and we have to persuade those people that better outcomes for their young people, for the future of their communities, doesn't lie with that far-right populism that has been peddled.
"We have to win that argument and try and persuade people back. The easy enemies that they identify are no substitute for answers, but we have to make sure that we do not enable that politics in any way.
"So I can say that we are open to discussions with other parties, and we should be.
"We have to recognise that political arithmetic is the way it is, and make sure that we put in place Labour values, Labour policies wherever we can, but not at the cost of working with people who, frankly, I think, challenge the very soul of the country."
