There would be "an almighty parliamentary row" if laws on assisted suicide were re-examined, Conservative MP Mark Pritchard has said.
The former secretary of the 1922 committee of backbenchers said Tory MPs would "not accept reform lying down".
His comments come after new health ministers Anna Soubry and Norman Lamb suggested there was a case for reassessing legislation.
The British Medical Association (BMA) said it opposed any change to the law.
Earlier on Saturday, newly-promoted health minister Anna Soubry told the Times it was "ridiculous and appalling" that Britons had to "go abroad to end their life".
Ms Soubry, Conservative MP for Broxtowe, said those seeking help to die should be allowed to obtain assistance in the UK.
She rejected euthanasia, but said "you have a right to kill yourself".
Her Liberal Democrat colleague Mr Lamb added that he also believed there was a "strong case" for the law to be reconsidered.
However, Mr Pritchard responded by saying that attempts to change the law would be met with fierce opposition and would cause "an almighty parliamentary row".
"Parliament writes the laws of the land not the CPS [Crown Prosecution Service] or individual ministers," he said.
"Any new right-to-die legislation will be rigorously fought by MPs from across the House.
"This is a slippery slope, which incrementally and over time, will reduce the 'right to life'."
BMA president Baroness Hollins also criticised moves to re-open the debate, and made it clear the medical profession did "not support a change in the law".
Speaking to Sky News, she said: "To change the law would be to change the boundary between life and death altogether. That's a journey I just don't want us to even start out on in this country."
The Department of Health said the views expressed by Ms Soubry were her own, and the Ministry of Justice said there were no plans for the government to change the law.
It was a matter for Parliament to decide, the justice ministry added.
Campaign group Dignity in Dying said it was currently consulting - along with the all-party parliamentary group on choice at the end of life - on a proposed draft bill.
In January, the Commission on Assisted Dying - led by Lord Falconer and set up and funded by campaigners who want to see a change in the law - said there was a "strong case" for allowing assisted suicide for people who are terminally ill in England and Wales.
But the report had a mixed response, with critics calling it biased.
Paul Tully, of campaign group SPUC Pro-Life, warned that if assisted dying was legalised people with disabilities would be faced with "the sickening prospect that if they struggle with suicidal feelings they will be given help to die instead of care and support".
"Such a move would allegedly save huge amounts of public funds in the costs of caring for disabled, elderly and supposedly unproductive people," he added.
"Disabled people must speak up now before the minister starts trying to legislate against their equal right to exist."
The debate over assisted suicide has resurfaced after Tony Nicklinson, a man with locked-in syndrome, died a week after losing a legal bid to end his life.
Assisted suicide currently carries a sentence of up to 14 years' imprisonment.
The law currently draws a crucial distinction between doctors deciding not to provide or continue treatment, which might prolong life, and acting to end a life, by for example administering lethal drugs.
Following the decision by High Court judges with regards to Mr Nicklinson, the BMA had said the court made "the right decision".
"The BMA is opposed to the legalisation of assisted dying and we are not lobbying for any change in the law in the UK," it said.
Mr Nicklinson's wife, Jane, meanwhile, has said she will appeal - as his widow and carer - against the High Court decision on his behalf because "nobody should have to suffer like Tony did".
Mrs Nicklinson, from Melksham, Wiltshire, said: "It is too late for Tony but I hope that we can now help those who find themselves in a similar position."