The group drew media attention for its campaign of settlement demands against individual buyers as well as sellers of embroidery patterns and software.
The October 17 letter further claimed that buyers, by purchasing and possessing unlicensed copies of embroidery software or patterns, had violated United States copyright law.
In the new lawsuit, the ESPC alleged defamation, intentional infliction of emotional distress, conspiracy, business disparagement, and tortious interference.
The ESPC subsequently petitioned for a subpoena seeking the identities of every subscriber to the two critics' Internet mailing list.
Prior out-of-court settlements show that the alleged infringers handed over lists of buyers and individuals to whom the machine embroidery designs were sent.