Church leaders in West Yorkshire are due to condemn the policies of the British National Party in a letter.
Church leaders believe the BNP will campaign actively in their area
They are urging people to vote only for those who show "a spirit of inclusive welcome" to all races and faiths in June's local and European elections.
Unless voters turn out in high numbers, they believe those with "extremist views" could be elected by a minority.
The letter, from the West Yorkshire Ecumenical Council, is being described as a historic joint statement.
The council is particularly worried about the far-right BNP's campaigns in the area ahead of upcoming elections and is urging church leaders to sign the statement at a chapel in Armley, Leeds, later.
Its executive secretary Dr Stephanie Rybak said: "If we do not want to be represented on the local council or in the European Parliament by a BNP candidate then we must vote.
"That is the message being put across by this statement, which has the
support of all the churches of West Yorkshire."
The BBC's religious affairs correspondent Robert Piggott said the West Yorkshire area had a history of periodic tensions between ethnic groups.
The church leaders feared the sometimes heated debate over immigration and asylum could allow the BNP to do well, he said.
One of the signatories, the Bishop of Ripon and Leeds John Packer, said they had been encouraged to take an overt political line partly by the example shown by the Archbishop of Canterbury Rowan Williams.
Church leaders were encouraged by Archbishop's stance
Dr Williams last week accused Prime Minister Tony Blair of weakening political trust by his handling of the war in Iraq.
The Bishop of Shrewsbury Alan Smith said the letter to church-goers warned apathy and complacency could hand victory to the BNP.
The two bishops will be joined by the Right Reverend Arthur Roche, of Leeds' Roman Catholic Church, and the Reverend Michael Townsend, chairman of Leeds' Methodist Church .
Also due to sign are Reverend Arnold Harrison, Moderator of the United Reformed Church, and representatives of the Baptist church and the West Yorkshire African-Caribbean Council of Churches.