What was once considered a safe and inexpensive haven for those with nut allergies has become the target of a bitter backlash from parents.

Fast-food giant McDonald's announced on Jan. 17 that the company will be using nuts that are not individually packaged in some of the products on its menus in Canada, starting with the popular Skor McFlurry. It warned that the possibility exists for cross-contact between nuts and other menu items.

"Shame on you," wrote a parent on the Facebook page of Food Allergy Canada, where the hashtag, #NotLoveinit quickly started spreading.

"Sad day. Bye-bye McDonald's, after 22 years relying on your safety policies," wrote another.

Adding peanuts and tree nuts to menu items was described as a "terrible decision" by Queen's University marketing expert Monica LaBarge in an interview on CBC Radio's The Current last Thursday. She said it was "totally perplexing."

The Skor McFlurry contains chopped almonds in the pieces of chocolate. The fast-food chain warns that the possibility exists for cross-contact between nuts and other menu items. (Tyson Koschik/CBC)

"We're hoping that the other food service operators will see the opportunity of continuing to provide what the general population wants," said Laurie Harada, the executive director of Food Allergy Canada. "Keep in mind there's 2.5 million-plus with food allergies."

LaBarge sees a golden opportunity for other fast-food chains.

"I would be gleeful if I was A&W and Wendy's because they've just handed you an opportunity. You've sent that many people somewhere else."

2.5 million Canadians have food allergies

So what are the 2.5 million Canadians with food allergies to do?

Harada, who has a son with nut allergies, said it's up to parents to decide if they continue going to McDonald's or not.

"We're not telling families, don't go to McDonald's," she told CBC News. "At the end of the day, they've got to make those decisions where they want to go.

"And we know from some of the consumers, they're going to go there and they should be asking questions."

She said parents have to be vigilant and vocal.

"It's important to tell the CEO what this specifically has meant for their families and what it means if they can't go there."

On Monday, Food Allergy Canada released an open letter it sent to McDonald's.

"There are immediate steps you can take to regain our trust. You can let us know which practices you will continue to have in place to minimize the potential for cross-contamination in your restaurants. You can also only use the 'may contain' statement on products as needed so it is not a blanket statement on all of your menu items," the group said.

Tim Sly is an epidemiologist and a retired professor from Ryerson University's Centre of Studies in Food Security.

He wonders whether the vitriolic backlash from parents, and families will force McDonald's to reconsider its decision on nuts.

"It's possible with the backlash we've seen that the McDonald's corporation, which is usually quite sensitive to the public's opinion, may reverse it. I wouldn't be at all surprised," he said.

When contacted for this story, McDonald's referred CBC News to its original announcement on nuts.