Keirin has been part of the Olympic Games since 2000. Documents given to the BBC suggest that $3m (£1.5m) was paid by organisers of a Japanese cycling event to the Cycliste Internationale (UCI) - the world cycling body.
According to the BBC then-president Hein Verbruggen denied any wrong doing.
The payments were allegedly made in the 1990s. The event was supported for inclusion into the Games by the UCI, and admitted in December 1996.
Keirin is a big event in Japan and also involved a lot of money. Fans can bet on the riders like in horse racing.
In the 1980s keirin was added to the world track championships organised by the UCI. Set to be dropped from the Worlds after the 1992, keirin celebrated a remarkable turnaround. Four years later it was part of the Olympics.
With Japan having a lot of money from the money making keirin events, there is some question about how much influence Japanese officials took on the UCI.
Cyclingnews will have more on the story as it unfolds.