A guide posted to voters to help them understand how to vote in the EU referendum has been condemned as biased for picturing a pencil over a vote for "remain".
Bristol City Council sent out the packs to its resident that included a segment helping people vote by post.
The leaflet quickly came to the attention of Brexiteers. The Leave.EU campaign began tweeting to ask people when and where they had received them, for fear they have been distributed beyond Bristol.
Mike Hookem, a Ukip MEP, told the BBC: "Any ballot papers which have gone out with marks showing either remain or leave boxes being ticked in the example need to be recalled and the person responsible needs to be investigated" Mr Hookem said.
"It may be an isolated incident around Bristol but in the interests of democracy we cannot take that risk."
The Electoral Commission said it "unlikely" people would vote differently because of a drawing of a pencil over the alternative choice but said the form "shouldn't have been used".
A spokesperson said: "We are following up with the counting officer for Bristol City to ensure that it is amended before any further postal voting packs are issued to voters in the area."
Bristol student Henry Michallat, who stood as a Conservative candidate in the local elections, told The Daily Telegraph: "I am appalled by it. It should be neutral.
"When you see that bit of paper, if you are not used to it or you are a first time voter, that might imply 'you should vote remain' and put the cross in the box."
The council said it would amend the forms "given current sensitivities".
"This form is designed to explain the logistics of voting by post and not to suggest how someone should vote," a spokesman told the BBC.
"The placement of the pen graphic was entirely incidental and we do not believe that anybody could reasonably be influenced by such a graphic.
"However, given current sensitivities, for all future postal vote dispatches the form and graphic will be amended."
BBC Politics reporter Brian Wheeler wrote: "The Electoral Commission has told Bristol council not to use it again. But with reports of similar leaflets dropping on doormats around the country it may be too late to do anything about it."