The latest suit, filed by InterCosmos Media Group, charges VeriSign with sending deceptive domain registration and renewal notices to customers of InterCosmos' directNIC.com registry site.
The suit comes on the heels of similar accusations made by BulkRegister.com, which lodged a lawsuit against VeriSign in May.
In both cases, VeriSign has been accused of sending marketing material that misleads its rivals' customers into thinking that their domain name is about to expire, and instructs them to renew with VeriSign.
InterCosmos filed suit in a Louisiana federal court last week, claiming to have lost profits and customers as a result of VeriSign's "trickery". The company is seeking damages for lost profits, restitution, mental anguish and attorneys' fees.