An unlikely lawsuit started as Citigroup filed a complaint against AT&T, which the credit card company says is infringing upon its trademark.

AT&T did not steal Citigroup's logo or slogan or anything of the sort, but it did have the audacity to use the word "thanks" in a campaign addressing customer-loyalty. The bank sued the telecom company, underlining the fact that it has secured a trademark for the word "thanks" some years ago.

This is not a late April Fool's Day joke, although we really wish it was.

According to the legal complaint that was filed in a Manhattan federal court, AT&T's campaign infringes a few of the trademarks of Citigroup. For example, the credit card enterprise owns both "Citi ThankYou" and "ThankYou." Gizmodo showcases a picture of the patent, in case you need to see it to believe it.

As a reminder, Citigroup has been making use of the "ThankYou" trademark since 2004, when it began a customer-loyalty program. The company says that over seven million of its clients have credit cards with the ThankYou slogan written in big letter across them.

Such numbers stand witness to Citigroup's position as global leader in credit-card lending.

According to the legal issue, Citigroup thinks that AT&T's campaign has a chance to confuse some of its own customers. What is more, the suit points out that the trademark designs borrows some inspiration from the fonts and word placements.

On the other hand, AT&T rejects the claims of the credit-card lending company.

"The law does not allow one company to own the word 'thanks,'" says AT&T's spokesman, Fletcher Cook.

Cook notes that the company is committed to keep thanking its clients, regardless how much this distresses the credit card company.

AT&T deployed its new loyalty program for customers on June 2. The complaint notes that the data carrier knew that Citigroup had similar trademarks in effect, but continued with its campaign anyway.

Citigroup mentions that its own "thankyou" programs are counting roughly 15 million members in the United States. About 1.7 million of the customers own credit cards which AT&T and Citigroup branded together.

Should you want to peruse the legal issue at your leisure, you only have to search for Citigroup v. AT&T, 16-cv-4333. The suit was filed under the U.S. District Court, at the Southern District of New York (Manhattan).

AT&T is no stranger to lawsuits, but some of them actually seem to be grounded into common sense. About one year ago, AT&T locked horns with the FCC on account of data throttling.