Sprint is taking AT&T to court for its decision to brand some of its 4G LTE networks as “5G E.” The lawsuit attests that subscribers will incorrectly assume that AT&T’s current phones support 5G and that their 4G LTE networks are 5G.

Sprint seeks damages to offset the loss of sales it’s suffering due to AT&T’s actions. Also, the company seeks to prevent AT&T from branding anything as 5G E that doesn’t adhere to the agreed 3GPP 5G specification.

AT&T uses the logo to indicate the sections of its 4G LTE network with faster LTE Advanced and Advanced Pro technologies support.

However, the 40Mbps speed of this 4G tech is very similar to what 4G LTE already offers, and falls short of the speeds 5G will one day be able to achieve.

Mobile carriers have united in condemning AT&T’s 5G E branding but this was limited to strongly worded statements and a single well-placed sticker until now.

In spite of all the criticism, John Donovan, CEO – AT&T Communication stood tall when he spoke at CES.

“I love the fact that we broke our industry’s narrative two days ago,” the CEO said, and dismissed the criticism as coming from his “frustrated” competitors.

Responding to the lawsuit, Randall Stephenson, CEO – AT&T told CNBC, that “we feel very comfortable with how we’ve characterized the new service that we’re launching,” and said that he believed the company is, “being very clear with our customers that this is an evolutionary step.”

AT&T might have been able to wave away previous criticism, but a fully-fledged lawsuit might be another matter if the courts are sympathetic to Sprint’s complaint.