Following months of speculation and rumors, Andy Rubin finally unveiled his Essential smartphone last week. And while there's no word on when the $700 handset will ship, the Android co-founder could already be facing a legal battle.

Spigen, a popular, US-based smartphone accessory maker, has written to Rubin's company accusing it of trademark infringement over the term "Essential." Spigen already has a line of Essential products that includes portable chargers, Bluetooth headphones, and battery cases, and it claims the Essential phone will "cause confusion." The company's lawyers note that Essential's own attempts at registering the trademark were twice denied by the US Patent and Trademark office for this very reason.

Spigen registered the trademark in August 2016. It's an International Class 9 mark, meaning it's related to computers, scientific devices, and smartphones.

The cease and desist letter demands that Rubin's firm stop using the term "Essential." If a response isn't received by June 15, Spigen will take "any and all actions" to protect its marks.

Considering the amount of media coverage the Essential phone has received, it's unlikely that the company will be prepared to change the name at this late juncture. Considering it had two trademark applications turned down in the past, one would imagine this situation is an eventuality it was prepared for.

Essential's official response to the matter is that Spigen's "assertations" are "without merit."

"Threat letters are commonplace in our sector. While it's Spigen's prerogative to make assertions, Essential believes they are without merit and will respond appropriately," said an Essential spokesperson. It looks like this one could be heading for the courts.