A total of 42 councils have signed a charter aimed at eradicating modern slavery in their supply chains.
The ten-point Co-operative Party Charter Against Modern Slavery commits signatories to train their procurement teams in ethical principles and scrutinise unusually low-cost tenders.
It means they must make sure suppliers comply with the Modern Slavery Act 2015 and protect whistleblowers.
The Co-operative Party, which is linked to the Labour Party, says that while most councils which have signed are Labour-run, the charter has received support across the political spectrum.
Conservative-controlled Surrey County Council and Cherwell District Council having both supported the charter, while in Scotland, SNP-controlled Dundee and SNP/Labour-controlled Edinburgh have agreed to implement it.
Co-operative Party general secretary, Claire McCarthy, said: 'Since Manchester cotton workers boycotted slave-grown cotton during the American Civil War, campaigning for justice and fair trade have been in the co-op movement’s DNA and we are very proud about that the charter has been adopted by so many councils across the country.
'The charter campaign is a testament to the effectiveness and persuasiveness of the 700 Co-operative councillors who have been pushing for implementation of the charter in town halls across the country.'