The lawyer for one of Canada's largest franchise companies is demanding a Calgary restaurant stop using the slogan Taco Tuesday.

Blanco Cantina on 17th Avenue S.W. has been using the phrase to advertise its half-price tacos on Tuesdays since it opened three years ago, said spokesperson Kate Mitchell.

But she says the restaurant received a letter from Quebec-based MTY Group — the franchisor of Taco Time Canada and dozens of other fast food brands — saying it holds a trademark on Taco Tuesday.

"MTY reserves its rights to be indemnified for damages suffered as a result of your unauthorized use of its trademark," the letter says.

Restaurant posts tongue-in-cheek petition

Mitchell said she found the letter very surprising.

"I didn't think that someone could own Taco Tuesday. It's so widely used," said Mitchell.

The Calgary restaurant uses the phrase online, on its menu and on a billboard outside the business.

Mitchell says the owners aren't going to pick a fight with the big national chain.

"We will comply with their request to not use it, but we're going to have some fun with it, because it really is quite funny," she said.

Blanco posted a tongue-in-cheek online petition to save its slogan, and a contest for customers to pick a new one. By end of day Monday, it said more than 100 people had signed the petition.

"Will this petition actually make any difference? Probably not," the website says. "But it will be fun to see how many taco lovers we can rally!"

"Our taco special isn't going anywhere," the page continues. "What should we call the beloved day of the week when everyone on the planet eats discounted tacos?"

A quick online perusal turned up lots of other Calgary eateries promoting Taco Tuesdays, including the Joyce Irish Pub on 4th, Julio's Barrio in Kensington, and National on 17th.

The trademark crackdown also came as a surprise to people who spoke to CBC News outside Blanco.

"Well then everyone needs to stop using the term," said Otto Guerli.

"I think it's very common. Are they going to start suing everyone who uses the term Taco Tuesday?" said Chris Potter.

Some also said they'd boycott TacoTime.

Dear <a href="https://twitter.com/TacoTime?ref_src=twsrc%5Etfw">@TacoTime</a> , for being so incredibly petty and for trying to “own” a phrase that is in wide use everywhere, I promise I will go to <a href="https://twitter.com/hashtag/TacoTuesday?src=hash&ref_src=twsrc%5Etfw">#TacoTuesday</a> everywhere EXCEPT Taco Time! 🖕<a href="https://t.co/1wupHxYZqw">https://t.co/1wupHxYZqw</a> <a href="https://t.co/kovgd7PWN3">pic.twitter.com/kovgd7PWN3</a> —@Got2sayso

South of the border, Wyoming-based Mexican food chain Taco John's has held the trademark for "Taco Tuesdays" in 49 of 50 states since 1989 and has fired off hundreds of cease-and-desist letters to other restaurants since then.

MTY Group did not respond to a request from CBC News for comment.