Popular mobile payments start-up Square has issued a cease-and-desist letter against a U.K. rival.

While the letter, embedded below, does not refer to similarities in products, it does address mPowa’s online use of a photo that Square finds similar to one on its own website. The letter was written by Square attorneys Fish & Richardson and directed at mPowa's CEO, Dan Wagner.

The letter accuses the newer mobile payment company of deliberately copying the promotional photo, but also seems to hint at greater issues of duplication between the two companies.

It states: “Indeed, it appears that mPowa’s infringement is intentional and deliberate, and that mPowa’s attempt at imitation may extend to other key Square intellectual property, including the Square Website and Square’s trademarks and trade dress.”

The skirmish is a sign of the growing competition within the mobile payment sphere, with mPowa launching recently in the U.S. and Square reportedly set to go international, according to TechCrunch.

Wagner defended his company's behavior to TechCrunch. “We think this is a petty attempt to divert our focus from trying to capture a meaningful share of the mobile POS market,” the mPowa chief told the website. “It won’t deter us from our focus, and everything contained in the legal missive is completely unfounded.”

At press time, Square had not responded to Inc.'s requests for comment.