In the lawsuit filed in Brooklyn federal court, Cablevision accused Verizon of running a deceptive advertising campaign that misrepresents the current performance of Cablevision's high-speed Internet.
Verizon's advertisements claimed a new study from the Federal Communications Commission showed Cablevision delivers up to only 59 percent of its advertised Internet speeds during peak hours, the complaint said.
The suit accused Verizon of relying on the speed test results from an obsolete August 2011 report that the FCC has since updated. Cablevision said more recent FCC tests in September and October show Cablevision delivers Internet speeds "very close to, and often above" what it advertises.
Verizon said its ads are based on the FCC's months-long study of Internet speeds, released in August.
"In terms of the accuracy of its advertising, Cablevision was the worst," Verizon spokesman William Kula said in an email, adding that the company would vigorously defend the lawsuit.
Cablevision is seeking a court order blocking the ads as well as monetary damages to be determined at trial.
The case is Cablevision Systems Corp et al v. Verizon Communications Inc et al, U.S. District Court, Eastern District of New York, No. 11-5934. (Reporting by Terry Baynes; editing by Carol Bishopric)