Police are investigating a leaflet supporting George Galloway's Respect party which claims Labour is "a party of closet racists".
The leaflet, which the Guardian reports was sent to Asian households in Rotherham, urges voters to choose Respect in the forthcoming 29 November by-election.
Under the title 'Respect Yourself' the leaflet, which was called "vile" by the website Labourlist, , claims the party is "corrupt" and "traffics in anti-islam bigotry."
But a spokesperson from Respect has said that the leaflet was not "in any way sanctioned by Respect or by our candidate Yvonne Ridley", and was instead a "badly-produced and rather transparent forgery."
"The document is a fake and clearly the latest in an ongoing dirty tricks campaign that we have experienced," they told The Huffington Post UK.
Labour MP for South Yorkshire and former home secretary David Blunkett said the leaflet was a "disgrace", alleging Respect had used similar claims in previous elections "and now they are trying to fool the people of Rotherham with them.
"If Respect claim this is not something they have produced then they must immediately distance themselves from it and make this clear in their leaflets."
During the by-election won by George Galloway earlier this year in Bradford West, Respect were accused of sending out leaflets to residents claiming: “God KNOWS who is a Muslim and he KNOWS who is not. I, George Galloway, do not drink and never have.”
A spokesperson for South Yorkshire Police said: "Police can confirm they have received an official complaint and the matter is currently subject to investigation and it is not appropriate to comment further at this time."