Government proposals to split the Home Office's work between two departments have been criticised by church leaders.
John Reid said the move was needed to meet today's challenges
Four Church of England bishops were among those who signed a letter to the Times newspaper claiming that the changes will harm asylum seekers.
They wrote that the changes would mean more would suffer from an "increasingly draconian immigration policy".
Home Secretary John Reid has said the Home Office needs to be split to meet the "challenges of today's world".
Next month, the Department for Constitutional Affairs will take over responsibility for criminal justice and be renamed the Ministry of Justice.
Mr Reid's Home Office will retain control of immigration, security, policing, counter-terrorism and ID cards.
The church leaders warned that the proposed scheme would increase the risk of bad decisions over refugee applications.
The letter said: "We are profoundly concerned about the increasing risk to our nation's public and political life of the inhumane and imperfectly processed decisions that are likely to result from the rushed reorganisation of the Home Office.
"We fear that yet more upheaval in the Home Office may result in greater casualties among those suffering from the brutalities of the government's increasingly draconian immigration policy."
The letter was signed by Michael Scott-Joynt, Bishop of Winchester; Thomas Wright, Bishop of Durham; Christopher Hill, Bishop of Guildford; Peter Selby, Bishop of Worcester and Bishop to HM Prisons; The Rev John Vincent, leader of the Ashram Community and ex-president of the Methodist Conference and the Rev David Cornick, general secretary of the United Reform Church.