Revd Jonathan Somerville, of Tabernacle Baptist Church Wolverhampton is one of the signatories.
He told Premier that Rob Marris MP is: "A really good man and a great MP - but I think he's naive about human nature and our sense is that human nature tells us they'll be a further act that extends the provision in this."
So far more than 34 Wolverhampton church leaders, representing more than 4000 local Christians, as well as four leaders with regional responsibilities, have signed the letter.
Revd Somerville added that: "We've got to find ways of agreeably disagreeing, and I hope that's what we're doing here.
"Rob Marris, I treat him like a brother - he's a good man, a fine politician, but on this issue I heartily disagree with what he's standing for."
When asked about the way the community felt after electing Mr Marris to power, Revd Somerville said: "There is a bit of surprise, it wasn't something he'd particularly spoken of a lot in campaigning, in fact none of us can remember him speaking of that so there's some surprise, and concern - that the MP of our city would do that."
The letter criticises a number of elements of the Bill, including the proposed safeguarding procedures and the fragility of human life.
It reads: "The main argument for your Bill is predicated on the basis that the law as it stands is being broken by anyone helping the terminally ill to die and that those who do so deserve to be protected by the law.
"The fundamental principle that they are breaking is that all human life is valuable and should not be taken away."
The idea behind the Bill is to allow the opportunity for terminally ill people to prescribed lethal drugs if they want to die early.
If passed, it would mean those with less than six months to live would be allowed to ask for a lethal prescription of drugs, as long as two doctors agree the patient has a "clear and settled intention" to die.
Their decision would be reviewed by a High Court judge in each case.
The Bill does not differ from a previous bill proposed to the House of Lords by Lord Falconer last year, but it adds the requirement for a High Court judge to approve applications for suicide within a fortnight of them being made.
Last month the former Archbishop of Canterbury, Lord Carey, exclusively told Premier why he has changed his mind on assisted dying.
The senior Anglican clergyman said he felt he had to explain to his friends who were "very surprised" and "very disappointed".
"The first is the fact of pain," he said.
"We have in this country one of the finest palliative care systems in the world, there's no doubt about that."
He added: "Never the less, in spite of that, people do suffer and many cancer patients experience excruciating pain."
Rob Marris MP, speaking in June, said: "The public are clearly in favour of a change in the law and it is right that Parliament now debates this issue.
"Lord Falconer's Assisted Dying Bill won two key votes and showed there was clear support amongst peers for law change, the only barrier in the way was one of time. I will be bringing a Bill forward in the Commons in light of the success of Lord Falconer's Bill and its unfortunate placing in the Lords ballot, which has denied peers the opportunity to finish what they started.
"Alongside the vast majority of the public, I am in favour of terminally ill people who are of sound mind having choice at the end of life.
"It is a choice that I would want for myself and I do not think we should be denying this to people who are facing an imminent death.
"The House of Commons has not voted on this issue for almost twenty years. While the prospects of getting the law changed are difficult without official Government support, this is an opportunity to show we in Parliament are not ducking our responsibility to the public and I look forward to continuing the case for a compassionate assisted dying law."
Cardinal Vincent Nichols, from the Roman Catholic Church in the UK made this statement: "This Private's Member's Bill seeks to legalise assisted suicide in England and Wales. It will have its Second Reading debate in the House of Commons on Friday 11th September 2015.
"The intrinsic value of each human life will be gravely undermined if this or any bill to legalise assisted suicide were to become law. I urge Catholics, as active citizens, to contact their local MP about this most important issue before the vote.
"Each of us is made in the image of God. The life of every individual is equally valuable (Genesis 1:27). Licensing doctors to supply lethal drugs to terminally ill patients to help them commit suicide rests upon the premise that some lives are worth less than others. It is therefore contrary to human dignity. It is also contrary to the 'do no harm' principle that underpins all medical practice. Helping someone to commit suicide compromises the fundamental human dignity of both parties involved. Assisted suicide is assisted killing.
"Those who are seriously or terminally ill deserve the best care that our society can give and must never be made to feel that they are a burden. We seek to support people in these circumstances, to the best of our abilities and resources. Palliative and end of life care have undergone significant advances in recent decades and we urge the government to continue to develop these services.
"A further profound anxiety has to be considered. If assisted suicide becomes legal, it will be impossible to ensure that people's decisions will not be influenced by many kinds of pressure or coercion, not just from others but from within themselves.
"The dangers inherent in changing the law are reflected by the significant opposition of medical professionals.
"MPs will face many different pressures in deciding how to vote. We will keep them in our prayers."
Listen to Premier's Hannah Tooley speak to Revd Jonathan Somerville here:
