Reforms to the coroners' system in England and Wales cannot succeed without a major increase in resources, says the British Medical Association.
The reforms were prompted by the Shipman case
The plans would see doctors employed full-time as medical examiners to improve detection of unnatural deaths.
Families would also be given greater powers to query information on death certificates, and to challenge the outcome of inquests.
The government said no firm decisions had yet been taken.
The proposed reforms were put forward following recommendations made by the inquiry into murders by former GP Harold Shipman, who signed the death certificates of many of his victims.
They are currently being assessed by the House of Commons Constitutional Affairs Committee, prior to the publication of a draft Coroner's Bill in June.
The proposals would see the creation of a chief coroner - an equivalent to the Lord Chief Justice's role among judges - and a chief medical advisor to provide expert input on medical matters.
It is also proposed to a move to a system of full-time coroners, all of whom will have to be legally qualified.
But the BMA is concerned about the feasibility of employing medical examiners to study case notes for each case in detail, and to discuss them with the consultant and relatives.
In its evidence to the committee, the BMA argues that without more staff, there would be long delays between the death and the coroner's verdict.
While the BMA agrees that reforms are long overdue, it says they would depend on an increase in funding and more doctors being encouraged to work in forensic medicine.
Dr George Fernie, chairman of the BMA's Forensic Medicine Committee, said: "The BMA has been calling for changes to the death certification system since 1971, and the government's intention to give families more say is a positive step that should be welcomed.
"However, things will not improve without significant additional resources.
"The system being proposed will depend on many more doctors being available, yet forensic medical careers are currently not a popular career choice when doctors can earn more money in the NHS.
"Change is sorely needed, but we cannot realistically expect it to happen without adequate resources."
A spokesman for the Department for Constitutional Affairs said the exact nature of the reforms had still to be decided.
"The coroners' system is 800-900 years old and has not seen any large reforms," he said.
"It lacks accountability, consistency and clarity and there is a lack of focus on the bereaved. It is also weak medically.
"We need to address these problems, and it is not just a question of throwing money at it."
The proposed reforms currently apply to England and Wales only, although Northern Ireland has a similar coroners' system.
In Scotland responsibility for investigating sudden and unexplained death falls to the Procurators Fiscal.
Every year, around 200,000 deaths are reported to coroners in England and Wales.