It would be "criminally naive" to think the proposal wouldn't put vulnerable people at risk, a Church official told Premier.
The bill, brought by Labour MP Rob Marris, outlines how two doctors would have to independently confirm the patient was terminally ill and had reached their own, informed decision to die.
But the Church of England is encouraging Christians to email their MPs, asking them to vote against it.
It's national adviser on medical ethics, Brendan McCarthy, told Premier vulnerable people would "most certainly" be put at risk by the law.
"Some half a million elderly people are abused each year, now to think that if an assisted dying bill were passed that some of those wouldn't be put under pressure to think of ending their lives, I think, would be criminally naive," he said.
He added: "How do we make absolutely certain that someone isn't put under pressure by a relative who may have an interest in them ending their lives prematurely.
"But the other thing that you absolutely cannot safeguard against is the sensitive individual who feels that because of their illness they're becoming a burden".
Those who support the bill told Premier the UK was capable of building strong laws that would not be open to abuse.
Last week Premier exclusively revealed why former Archbishop of Canterbury Lord Carey had changed his mind, and was backing the bill.
He said: "There's nothing noble about excruciating pain and I think we need as a nation to give people the right to decide their own fate.
"In my view it is a profoundly Christian and moral thing to devise a law that enables people if they so choose to end their lives with dignity."
But Brendan McCarthy disagreed and said the Church was clear in its position fighting against the bill.
"The current Archbishop of Canterbury, there's no question at all with regard to his views," he said.
But he said the Church of England was "a Church that encourages people to make up their own minds".
He added that he wasn't worried this particular bill would become law but said campaign groups would keep "chipping away" until the law is changed.
"I don't think this particular bill will go through but it's important that people do approach their MPs to make their opinions known so that no complacency does creep in."
Listen to Premier's Antony Bushfield speaking to Brendan McCarthy here:
