Postal workers have refused to deliver election leaflets from the British National Party (BNP) as they are afraid they could cause offence to local residents.
About 100 workers in the West Country will not carry the leaflets because they bear an anti-immigration message.
The Communication Workers Union told the Times that Royal Mail was breaking a "conscience clause" agreed four years ago that allowed staff to refuse to deliver literature they find offensive.
Dave Wilshire, spokesman for the Bristol and District Branch of the CWU, said: "In Bristol we have the St Paul's area which has a very high density of those from ethnic backgrounds. Anyone being expected to post BNP stuff through there is going to feel at risk.
"Managers in Bristol are effectively bullying people."
He added: "Over the past 48 hours I've had around 32 calls from individual members and those speaking on behalf of groups, saying they don't want to deliver the material. That is fair enough. The clause says members don't have to deliver material if they feel threatened or if it is against their personal beliefs."
Workers ringing the union have accused Royal Mail chiefs in Bristol and Somerset of "bullying", with one office allegedly threatening workers with dismissal if they did not comply.
Simon Darby, BNP spokesman, said: "We have a contract with the Royal Mail to deliver some 29 million BNP leaflets. Some will be binned by Labour-supporting postmen who want to corrupt the democratic process, but it is a question of cutting that down."
Royal Mail said: "Where possible we will try to be flexible and sensitive to individual personal circumstances or beliefs. However, we need to balance this with Royal Mail's legal obligations under the Representation of the People Act, to deliver election material."