New York CNN  — 

The war over “Taco Tuesday” may be heating up now, but its origins date back several decades.

Regional chain Taco John’s owns the “Taco Tuesday” trademark, and last week it responded to a lawsuit from Taco Bell that aims to cancel the trademark. Wyoming-based Taco John’s said Taco Bell’s lawsuit is filled with “statements of opinion to which no response is required, including that Tuesday is a mediocre day of the week.”

How did a small Wyoming-based chain come to own the trademark? The story begins in the 1980s, when a Taco John’s restaurant owner coined the term “Taco Twosday” to advertise a deal of 99 cents for two tacos on its slowest day of the week.

It worked — so well, in fact, that the owner shared it with other franchisees.

The name was eventually tweaked to “Taco Tuesday” and the chain trademarked the phrase in 1989, making it part of its marketing. Since then, Taco John’s has defended its use of the phrase and sent cease-and-desist letters to others trying to use it.

“Over the years we’ve certainly asserted our trademark against national companies, restaurants big and small, and even pharmaceutical companies,” former Taco John’s marketing executive Billie Jo Waara said in a 2016 interview with the website Priceonomics. “We also recognize that the unauthorized use [of Taco Tuesday] is prolific, and we do our best to communicate ownership.”

It’s not only Taco Bell that wants to eliminate the trademark.

TacoTuesday.com, owned by a southern California restaurant group that chronicles those deals, said that having “‘Taco Tuesday” trademarked today can be likened to someone owning “happy hour” or ‘sunday brunch.’” The group also put together a “small collection of advertisements” from old newspapers dating back to 1966, which it says proves its point that Taco John’s shouldn’t own the trademark.

Still, Taco John’s owns the phrase (at least, it does in 49 states, as Gregory Hotel owns it in New Jersey thanks to the complexities of trademark law).

So that ownership is where the battle lies — and the fight is about to “get real,” according to trademark attorney Josh Gerben.

The next step in the legal process, which could last about two years, is the discovery portion. Gerben expects Taco Bell to “conduct a survey to determine what portion of the American public associated Taco Tuesday” with either Taco John’s or Gregory Hotel, “versus the phrase being a more of a general custom associated with eating tacos on Tuesdays,” he told CNN.

Gerben expects that Taco John’s and Gregory Hotel will likely conduct their own investigation as to whether or not Taco Bell has been “attempting to assist other restaurants or celebrities to use Taco Tuesday in an attempt to invalidate their trademark rights,” perhaps with a similar customer survey.

“This is not going to be something where Taco Bell is going to be able to declare victory anytime soon,” he said.