Using the phrase may land you a cease and desist letter from Taco John's.
Taco Bell is trying to free the phrase "Taco Tuesday," which is officially trademarked by a rival taco chain.
Taco John's, a fast food "West-Mex" chain based in Wyoming, has held a trademark on the commonly used phrase since 1989.
Since then, Taco John's has sent cease and desist letters to other restaurants who use it.
An advertisement for people to apply to a job at Taco John's on the chain's website encourages potential applicants to join the "Original Taco Tuesday" crew.
Now, Taco Bell is fighting for the right to have its own "Taco Tuesday."
The restaurant chain argues nobody should have exclusive rights to a common phrase.
The trademark appeal process at the United States Patent and Trademark Office can take up to two years.