The US is preparing to bring in legal changes giving Attorney General Alberto Gonzales new powers to limit the time inmates spend on appeal on death row.
The US carried out 53 executions of death row inmates last year
The change in the rules, under which Mr Gonzales will be able to decide state requests to speed the appeals process, was a measure in the 2006 Patriot Act.
Death penalty experts warn the move could affect death row inmates' chances of overturning wrongful convictions.
The US Justice Department has played down the significance of the new rules.
Spokesman Erik Ablin said they merely set out guidelines states would have to follow to qualify for a faster federal review of moves to limit death row appeals, a system authorised in 1996 but not implemented.
He said: "This has nothing to do with specific cases and the attorney general has no authority to change the certification requirements, which are determined by statute."
Under the new regulations, due to take effect after 24 September, prosecutors would be able to "fast-track" the death row appeal process if the state requests it and the attorney general, rather than a federal appeals court, agrees that the state has proper legal counsel in place for death row defendants.
Senate Judiciary Committee chairman Patrick Leahy, a Democrat, and Arlen Specter, the committee's top Republican, wrote to Mr Gonzales earlier this month asking him to extend the consultation period on the new rules.
"It is crucial that the legislative changes to this complex and heavily litigated area of the law be successfully and appropriately implemented, especially given the tremendous personal stake for individual defendants," they wrote.
Death penalty experts argue that shortening the time allowed for inmates to appeal, in what are often very complicated cases, will make effective and fair review very difficult.
US METHODS OF EXECUTION
Lethal injection: Authorised in 37 states (plus US military & federal government)
Electrocution: In 10 states (sole method in Nebraska)
Gas chamber: In five states (all of which have lethal injection as alternative)
Hanging: Only in New Hampshire and Washington
Firing squad: In Idaho and Oklahoma. It is available to inmates in Utah who chose it before the method was banned
Source: Death Penalty Information Center
The new procedure will cut down the amount of time that death row inmates have to appeal to the federal courts, once the state court has ruled, from one year to six months.
The federal courts will also have less time to review the cases before them, which represent the only opportunity defence lawyers have to file new evidence.
Elisabeth Semel, director of the Death Penalty Clinic at the University of California law school in Berkeley, told the BBC News website the new rules represented a "very dramatic change".
She fears that not only the few death row inmates who turn out to be innocent but also those who have been unfairly given the death penalty will lose out.
And, she points out, those who decide whether to limit the appeals process are the same people as are seeking a faster process.
"It's like giving control of the hen house to the fox, because it's the attorney general in the state going to the attorney general of the US and getting permission to do something that kills the chicken," she said.
Ms Semel also criticises the law for not defining what is meant by the state "having a system to provide competent counsel", which is the provision Mr Gonzales must agree has been met.
Jack King, of the National Association of Criminal Defense Lawyers, said the consequences of the law change would be "disastrous".
No state was ever signed off by the federal appeals courts under the 1996 law as meeting the requirements on providing adequate defence lawyers, he said.
Congress has now given that power to the attorney general who, Mr King said, was less qualified but more likely to approve states for the fast-track process.
The Judicial Conference of the US, which oversees policy for the federal courts, has voiced concern that the new rules will make it harder for federal judges to review cases properly.
Some death penalty critics argue Mr Gonzales, who has been under fire for his role in the dismissal of US attorneys, is not the right person to have sway over the death penalty process, particularly because of his legal background in Texas, which executes more people than any other state.
Fifty-three executions were carried out across the US last year, according to the Death Penalty Information Center. So far this year, there have been 32.
The number of executions hit 98 in 1999 but has been falling since amid legal challenges to the use of lethal injections and increasing use of DNA evidence to overturn convictions.
However, some state legal officials argue that moves to shorten the length of time inmates spend on death row are overdue.
Kent Cattani, a legal official in the Arizona attorney general's office, told the Los Angeles Times: "If you are going to have the death penalty at all, it shouldn't take 20-25 years."
The high cost of keeping inmates on death row is also cited by some conservatives as a reason to speed up the appeals process.
According to a 2005 Los Angeles Times study, it costs California $90,000 more a year to keep an inmate on death row than in the general prison population, adding up to some $57.5m extra each year.