Television Broadcasts is suing Asia Television for alleged libel after ATV said the city's top broadcaster had falsified its rating results.
In a statement TVB said it had filed a writ with the High Court against ATV after the broadcaster had failed to issue a public apology in relation to what it called unfounded accusations against TVB.
TVB stressed there was no falsification of its TV audience measurement survey and said the sampled households were selected independently by a research company CSM, and that TVB had not been involved in the selection process - directly or indirectly.
CSM was appointed the city's main ratings provider in March 2005 by an industry committee consisting of TVB, ATV and the HK4As.
The spat between the two broadcast groups originally started over ATV's exclusive coverage of the Hong Kong Film Awards. ATV partnered with the University of Hong Kong's Public Opinion Programme (HKU POP) to track viewer ratings on the awards, reporting a total audience or 2.3 million.
TVB's published figure for the same show was 440,000, representing a discrepancy of more than 1.85 million.
ATV criticised TVB's rating system as unreliable and called on the Broadcasting Authority to look into the issue.
ATV also suggested other research firms such as The Nielsen Company and HKU POP to be allowed to conduct audience surveys.
Senior vice president of ATV Hoi-ying Kwong said audience ratings have a direct impact on ATV's image and the current system has caused the station billions of advertising dollars each year.