KFC sued Church’s Texas Chicken for allegedly violating its trademark rights by using the term “original recipe” in its advertising.

The lawsuit, filed last week in federal court in Texas, alleged that fast food rival Church “suddenly” began using the brand to promote its fried chicken in September. Ads promoted on television, social media and on Church’s website include photos of the fried chicken line along with the statement, “Our original recipe is back.”

KFC said it sent a letter to Church’s in October objecting to the use of the phrase, but it was ignored.

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KFC has trademarked the phrase “original recipe” for more than half a century. In the lawsuit, the company said promoting fried chicken made with a “unique, signature flavor created by a secret blend of 11 herbs and spices” remains a cornerstone of KFC’s advertising.

“This combination of 11 herbs and spices is one of the most well-known, iconic trade secrets in the food industry. And it is this combination of ingredients that KFC promotes with its original recipe mark,” the lawsuit states. The statement was included.

KFC told the U.S. District Court for the Eastern District of Texas that Church’s continued use of the trademarked phrase in its advertising would likely confuse consumers and have a negative impact on its brands.