McDonald's Canada is adding nuts to the menu and says all of its food could be contaminated with a variety of allergens, sparking outrage from thousands of Canadians who live with or care for someone with serious food allergies.

The move is a major departure from the company's long-standing policy of serving nuts in sealed packages, which enabled people with peanut and tree-nut allergies to safely consume many items on the menu. In a statement posted on its website, McDonald's Restaurants of Canada Ltd. said that as of Tuesday, the company is adding nuts that are not individually packaged to the menu across the country.

"All products available at our restaurants may contain or come into contact with peanuts, tree nuts or other allergens," the statement said. The first item to feature nuts will be a new Skor McFlurry.

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Susan Waserman, an allergist at McMaster University in Hamilton, said the move is surprising because McDonald's has long been seen as a leader when it comes to allergies. For years, the restaurant carefully listed ingredients and made it easy for consumers to understand exactly what was in certain menu items. Dr. Waserman added that the changes are ambiguous. In its statement, McDonald's indicates that any of its menu items could come in contact with "other allergens" without clearly defining whether that includes dairy, shellfish or other allergens.

"There's not a lot of clarity about why they made such a wide-sweeping statement," said Dr. Waserman, who is also a food-allergy researcher at AllerGen, a national research network.

The news is spreading through those in Canada with allergies and thousands have taken to social media to voice their shock and displeasure with the decision.

"McDonald's has always been our fall back because we felt safe there," said Sheila Rusnell-Newton, a Calgary mother whose 15-year-old has severe peanut and tree-nut allergies. "This isn't just somebody who's pissed off because my kid can't eat a Big Mac any more."

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John Betts, chief executive officer of McDonald's Canada, said in an interview the chain is responding to growing customer demands for more diverse product offerings with nuts in them. He said McDonald's in Canada was "pretty unique" among the chain's other divisions in offering prepackaged nuts separately.

He said the latest move isn't a bid to simplify processes as the restaurant chain tests all-day breakfast in Canada. "We've had a long-standing commitment to a focus on allergens – that hasn't changed," Mr. Betts said. "We're still communicating to our guests [customers] and making them aware of things they need to be conscious of."

Marie-Josée Bettez, an author who runs a website about allergies, reported the news on her site's Facebook page, called Déjouer les allergies, last week after receiving an internal memo from McDonald's. Since then, more than 1,400 people shared the post and hundreds left comments. Ms. Bettez said the change is a major disappointment to many with food allergies who relied on the restaurant chain.

"McDonald's restaurants were one of the few restaurants where [people with allergies] could eat without being too stressed out," she said. "When you're on the road, for example, there's at least one place you can stop and it's safe."

Many frustrated consumers are also leaving comments on the McDonald's Canada Facebook page. As of Tuesday afternoon, the company had not responded to them.

It's unclear why the change is being made or whether the company plans to implement a similar policy in the United States. In November, the company conducted a pilot project offering Skor McFlurries with unpackaged nuts in two Ontario restaurants.

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Ms. Rusnell-Newton said her family often travels to visit relatives or to attend baseball tournaments, and McDonald's locations were a safe haven. It's difficult to safely eat out with a family member who has a severe food allergy and the change means one less option to count on, she said.

"It's a very big thing and unless you live it, there's no way to explain it to people."

Research has shown that about 2 per cent of Canadians have peanut allergies and 2.4 per cent have tree-nut allergies.

With a report from Marina Strauss