TORONTO - A union representing Ontario nurses is asking Canada's top court to overturn a ruling that left those who contracted SARS unable to sue the provincial government over the deadly outbreak six years ago.

The Ontario Nurses' Association is asking the Supreme Court of Canada for an appeal of the May decision by Ontario's top court, the union said Thursday.

The ruling leaves nurses at risk as they care for patients during the current swine flu pandemic, as well as other outbreaks of potentially deadly diseases, the union said.

So far, 63 Canadians have died after contracting swine flu, also known as the H1N1 virus.

"The decision is particularly disturbing in the context of we're now into the next pandemic," said Elizabeth McIntyre, a lawyer representing the nurses and their families.

"We are going to be relying on the nurses to be there on the front line."

Several groups attempted to sue the province, alleging the government put economic interests ahead of public safety during the SARS outbreak which claimed 44 lives in the Toronto area.

But the Ontario Court of Appeal said the claims did not have legal grounds to proceed, and dismissed the lawsuits.

The nurses' claim involved 53 registered nurses in the Toronto area and their families, including the family of Tecla Lin, who died of SARS in July 2003.

They alleged the province failed to provide nurses with timely information and that the directives issued to Ontario hospitals were inadequate and exposed nurses to the risk of contracting SARS.

They also alleged Ontario declared the health emergency over prematurely to counter the effect of a World Health Organization travel advisory.

In its ruling, the court said Ontario is obliged to protect the public from the spread of communicable diseases, but can't be held financially responsible to people - including nurses - who catch those diseases.

"If we want nurses on the front lines during outbreaks that can kill them, who do they turn to provide the equipment that will keep them safe?" ONA spokeswoman Sheree Bond said Thursday.

Nurses have a professional responsibility to care for the sick, but unlike other workers, they are limited in their right to refuse to work, even when it places them in jeopardy, McIntyre said.

"So when they're walking into a room where you have a patient with swine flu, for example, they want to be able to rely on the direction they're given as to how to protect themselves from becoming ill," she added.

"That's important not just for them, but for the public generally, to make sure that we protect health-care workers. They're our front line of defence against pandemics."

Ontario declared SARS a provincial emergency on March 26, 2003, and by late April the province began to relax infection controls imposed on hospitals. The premier lifted the declaration of emergency on May 17.

However, on May 23 Ontario announced SARS had not been completely contained.

The group filed for leave for appeal on July 28, but it could take until the end of the year before the Supreme Court announces whether it will hear the appeal, she said.