Ms Englaro opposed being kept alive artificially, her father says
Italy's Senate is set to debate an emergency government decree to stop doctors withdrawing life support from a woman in a permanent vegetative state.
PM Silvio Berlusconi drafted the decree last week, but President Giorgio Napolitano has refused to sign it.
Doctors at a private geriatric clinic in Udine have withheld food from Eluana Englaro, now 38, since Friday. She has been in a coma since a 1992 car crash.
Doctors said her "path to death" would be irreversible by the end of the week.
"We are proceeding with the total suspension of artificial nutrition," Dr Carlo Alberto Defanti, Ms Englaro's neurologist, told the Ansa news agency on Sunday.
Dr Defanti described her condition as "stable", but said she was being given sedatives to calm muscle spasms.
Giuseppe Campeis, a lawyer for Ms Englaro's father, Beppino, said: "We are continuing with medical procedures aimed at ensuring a gentle death."
Medical experts quoted by the Corriere della Sera newspaper said the process should become irreversible within three to five days. Another report said it could take Ms Englaro about two weeks to die.
Italy does not allow euthanasia. Patients have a right to refuse treatment, but they are not allowed to give advance directions on what treatment they wish to receive if they become unconscious.
Beppino Englaro has been battling with the courts in Italy to let his daughter die since 1999, insisting it was her wish.
Italy does not allow euthanasia although patients can refuse treatment
In July, a court in Milan ruled that doctors had proved Ms Englaro's coma was irreversible. It also accepted that, before the accident, she had expressed a preference for dying over being kept alive artificially.
State prosecutors appealed against the ruling, but the Court of Cassation in Rome ruled the challenge inadmissible in November.
The Italian health ministry subsequently issued an order barring all hospitals in the region from withdrawing Ms Englaro's life support, but this was overruled by a court in Milan on 21 January.
Ms Englaro was previously cared for at a church-run hospital in Lecco, but was transferred to La Quiete geriatric clinic last week, after it said it would receive her and allow her to die.
The move provoked outrage from the Vatican, whose health minster described it as "abominable" and tantamount to murder.
Pope Benedict XVI described euthanasia as a "false solution" to the tragedy of suffering.
In a last minute move on Friday, Prime Minister Berlusconi drew up an emergency decree with the support of the Vatican to prevent doctors withdrawing her feeding tubes.
President Napolitano (left) said Mr Berlusconi had acted unconstitutionally
But President Napolitano refused to sign it on the grounds that the government could not arbitrarily overturn a legal ruling and that such a sensitive issue had to be fully debated by parliament.
Mr Berlusconi, who has a parliamentary majority, subsequently said parliament would enact a new law barring doctors halting nutrition to patients in a coma.
The Senate is expected to hold a vote on the matter on Tuesday, while the lower house, the Chamber of Deputies, could take up the bill as soon as Wednesday.
Meanwhile, Health Minister Maurizio Sacconi said on Sunday that the government believed La Quiete clinic was not qualified to help Ms Englaro die because it was primarily a rest home for the aged.
"The Milan appeals court spoke of a hospice or a sanitary structure, while here all we have are rooms on loan," he said. "It's an irregular situation."
Mr Sacconi also said he had sent a team of health inspectors to the home to investigate "irregularities" and observe Ms Englaro's care. The clinic's deputy director, Luciano Cattivello, told reporters that it fulfilled all legal requirements.
The Catholic Church has welcomed the government's attempt to delay Ms Englaro's death. Udine Archbishop Pietro Brollo asked people to pray for "the suspension of this tragic execution".