Radio boss Kelvin MacKenzie has launched a £66m legal action against the company which measures ratings, claiming they are "fatally flawed".
Kelvin MacKenzie says Talksport is missing out on advertising revenue
Former Sun editor Mr MacKenzie, who now runs Talksport radio, not using an electronic measuring system costs it £1.5m a month in lost revenue.
Talksport believes Radio Joint Audience Research (Rajar) underestimates the number of its listeners.
But Rajar has dismissed Talksport's claims as "ludicrous".
Its says the system - which depends on listeners filling out a diary - robs it of 4.7 million listeners each week.
Mr MacKenzie's company, The Wireless Group, has carried out its own survey of listeners using electronic measuring equipment, which puts its weekly ratings at 6.9 million - against 1.9 million through Rajar's system.
He says Rajar's figures damage his business because advertisers spend their money on stations which have higher ratings.
Mr MacKenzie said: "Incredibly, I have spent more than three years of my life trying to persuade the radio industry that the diary, pencil and short-term memory should be replaced by a technology that measures radio audiences more accurately.
"My opponents have tried desperately to kick the issue into the long grass because they are making a helluva lot of money out of this fraudulent system."
The Wireless Group also indicated it may also take legal action against Rajar's shareholders - the BBC and the Commercial Radio Companies Association.
Rajar trialled two electronic methods of recording ratings in 2002 and 2003 but subsequently decided against adopting them.
The Wireless Group believes the trial was not conducted properly and did not involve the public.
Rajar's figures for Talksport, using listener diaries, place Talksport behind Classic FM and Virgin.
But the system employed by The Wireless Group, where volunteers wear a wristwatch that detects radio sounds, make it the most listened-to commercial station.
Rajar managing director Sally de la Bedoyere said: "Rajar would contest the proceedings vigorously and refuted claims made in the The Wireless Group's press release.
"Leading counsel advise that it is highly likely that the claim will be struck out before it comes to trial.
"It is not surprising that the ludicrous claims relating to financial losses are for the purposes of a sensational press release, and are not detailed in the proceedings".