The Japan Rugby Football Union (JRFU) said on Monday it would scrap three rounds of matches after a player was arrested on suspicion of using drugs, insisting the cancellations had nothing to do with coronavirus.
JRFU chairperson Osamu Ota said top tier rugby matches for the coming three weekends until March 29 will be cancelled, adding he was "truly sorry for the fans".
Ota said there had been several arrests over the illegal use of recreational drugs in recent months, describing it as a "major issue that shakes the foundation of Japan's rugby world".
The most recent case came last week when Hino Red Dolphins revealed a player had been arrested on suspicion of using illegal drugs, without announcing a name.
Domestic media said it was a player from New Zealand who was suspected of using cocaine.
The JRFU said it will have to "thoroughly educate" teams about compliance with drug laws.
Drug cases are rare among sportspeople in Japan, where laws against illegal substances are strict.
The union has already postponed some matches due to the outbreak of the new coronavirus, which has killed 3 825 people and infected more than 110 000 in over 100 countries.
But the latest decision is "separate from the new coronavirus", Ota insisted.
The union will discuss again in late March when they will resume the matches.
The coronavirus has taken its toll on major sports events in Japan, with Prime Minister Shinzo Abe calling on organisers of large events to consider cancellations or delays.
On Sunday, sumo's spring tournament began without spectators, and this month's Tokyo marathon was held with elite runners only.
The big question mark hangs over the Tokyo Olympics, which are due to open on July 24. Organisers insist preparations are continuing as usual, but they have been forced to scale down some test events and the flame relay.