MONTREAL — A federal law that bans tobacco sponsorship, restricts advertising and requires large warnings on cigarette packs is unconstitutional, lawyers for Canada's three largest tobacco companies argued Monday.

Imperial Tobacco Canada Limited, Rothmans, Benson & Hedges Inc. and JTI-Macdonald Corp. began five days of hearings on an appeal of a Quebec Superior Court decision upholding the 1997 federal Tobacco Act.

The companies argued the law which prohibits lifestyle advertising effectively constitutes a total ban on advertising, something the Supreme Court of Canada ruled was unconstitutional in 1995.

The industry isn't asking for "unlimited freedom of advertising of tobacco products,'' lawyer Simon Potter said outside the courtroom.

"But there should be a small window, there should be some possibility for Canadians to receive advertising about products that they have a right to buy,'' said Potter, who's representing Imperial Tobacco.

The companies said a 2002 Quebec Superior Court ruling upholding the federal law failed to address several key constitutional issues and contained numerous factual errors.

The federal government, the Canadian Cancer Society and anti-tobacco advocates said they'll argue the law is constitutionally valid.

"The law permits informative advertising and brand preference, and that's the question that the court will have to answer,'' said government lawyer Claude Joyal.

Rob Cunningham, lawyer for the cancer society, said while the restrictions on advertising and promotion infringe on freedom of expression, they're justified as a reasonable limit under the Charter of Rights and Freedoms.

"We believe that these laws are essential to protect public health in Canada, to reduce smoking among adults and among children,'' said Cunningham.

"And it's working.''

The youth smoking rate at 18 per cent is the lowest ever recorded. Smoking among adults has decreased to 21 per cent, compared with 30 per cent before these laws were enforced, he said.

Global efforts since Canada's law was enacted shows it's not out of step with the rest of the world, added Cunningham.

"There are many countries that have laws stronger than Canada and even more will join that category.''<

Since May 2003, 168 countries have signed a World Health Organization agreement that once enacted would set international standards on tobacco price, tax increases, advertising, sponsorship, labelling and second-hand smoke.

The European Union, Thailand, Japan, Mexico and Australia are among 36 countries that have ratified the framework agreement that includes requirements for picture-based package warning.

Canada has not ratified the agreement that takes effect once 40 countries have ratified it. However, Canada requires that warnings such as pictures of diseased lungs occupy half the space on cigarette packages.

Australia requires 60 per cent of the package to contain warnings. Belgium's ratio is 56 per cent.

The Quebec Court of Appeal can only review evidence and pleadings introduced to the lower court prior to its ruling in 2002.

Despite the changes since then, Canada remains the most highly regulated countries in the world on tobacco advertising, said Christina Dona, an Imperial Canada spokeswoman.

"We still don't feel that the World Health Organization is talking about infringing rights, they're just calling for restrictions on advertising that we fully agree with,'' she said.

"We're just looking for a law that will allow us in some way to communicate with adult consumers in a way that is deemed appropriate.''