NMa, the Dutch competition watchdog, fine the three suppliers millions of euros.
Between them, the three companies account for 70 to 80 percent of the Dutch bicycle market.
Gazelle was fined EUR 12.9m. Batavus-maker Accell was fined EUR 12.8m and Giant was forced to pay a fine of just under EUR 4 m.
According to the NMa, the three companies entered into an illegal agreement to raise the recommended price of bikes in 2000-1.
NMa contends that the suppliers held price-fixing meetings in the summer of 2000.
Accell said the fine is "out of all proportion". It has lodged an appeal.
Accell does admit that there were meetings and costs were discussed but there was no price-fixing, said Accell's CEO Rene Takens.
"Price rises are not an agreement, but the logic consequence of [dollar /yen] developments," said Takens.
Giant and Gazelle claim that the fines are "ridiculous".
"The NMa is basing the fine on suspicions and does not come with hard evidence," said Gazelle director Klaas Dantuma.