CopyTele is targeting AT&T with a patent infringement lawsuit. Encrypted Cellular Communications Corporation, a wholly owned subsidiary of CopyTele, is alleging AT&T used its patented Encrypted Cellular Communications technology.

CopyTele has supplied encryption devices for use by the U.S. military.

On top of normal data and wireless charges, AT&T charges $115 per device and a $40 monthly fee for its encrypted phone service, according to CopyTele.

AT&T declined to comment on this matter.

CopyTele said in a statement that this is the sixth patent assertion case since shifting its business model away from technology development.

CopyTele CEO Roger Berman said that with more than 300 million wireless subscribers in the U.S. and the heightened desire for privacy, CopyTele’s patent assertion campaign has “enormous potential.”

Last year, CopyTele drew “patent troll” criticism when it filed a patent infringement suit against Microsoft over encryption technology used in Skype.