Ten Church of England bishops, including two from Yorkshire, are backing a change in the first-past-the-post voting system for "ethical and moral" reasons, campaigners said.
The Rt Rev John Packer, Bishop of Ripon and Leeds and the Rt Rev Martyn Jarrett, Bishop of Beverley said they will support changing the system for electing MPs to the House of Commons from first-past-the-post to the alternative vote (AV) in a planned referendum on May 5.
The AV system would mean voters are able to rank candidates in order of preference.
Jonathan Bartley, a spokesman for the Yes campaign for the AV system, said the bishops were backing change on moral and ethical grounds.
Under AV, MPs would have to win the support of a majority of voters rather than just around one in three, as is currently the case in two thirds of constituencies, he said.
"The bishops are frustrated that there is very little in the way of the moral, ethical dimension to this. The debate has been constructed so far in terms of which party will benefit and who is trying to gain an advantage out of this," he said.
"What the bishops are saying is that there are more important issues."
The other bishops to throw their weight behind plans to switch to the AV system are the Rt Rev Michael Langrish, Bishop of Exeter, the Rt Rev Alan Smith, Bishop of St Albans, the Rt Rev Nigel Stock, Bishop of St Edmundsbury and Ipswich, the Rt Rev Alan Wilson, Bishop of Buckingham, the Rt Rev Michael Perham, Bishop of Gloucester, the Rt Rev Colin Buchanan, former Bishop of Woolwich, the Rt Rev Peter Dawes, former Bishop of Derby and the Rt Rev David Atkinson, former Bishop of Thetford.
A deal between Tory and Labour peers was struck in the House of Lords yesterday over legislation introducing the referendum following protracted debate.
Labour peers have opposed measures contained in the same legislation to reduce the House of Commons from 650 to 600 MPs - which the party claims are designed to disadvantage it.