French rugby federation (FFR) president Bernard Laporte was placed in police custody for questioning on Tuesday as part of a preliminary investigation into suspicions he favoured the Montpellier club, owned by billionaire Mohed Altrad.
Altrad and the chief organiser of the 2023 Rugby World Cup to be held in France, Claude Atcher, were also placed in custody for questioning, along with two senior FFR officials.
Laporte, 56, a former coach of the France national team who is also vice-chairman of World Rugby, is suspected of pressuring the appeals committee of the French league, the Top 14, to reduce a disciplinary punishment against Montpellier in 2017.
The questioning comes as Laporte is standing for re-election as FFR chief with the result expected on October 3.
"With 10 days to go to a key deadline for our federation, an organised campaign of destabilisation is trying to take French rugby down," Laporte said in an open letter to clubs published on Facebook later on Tuesday.
"It's a true attempt at a coup of which there is no doubt about the motivation of the creators. It all adds up to a truly foul electoral strategy," he added.
Laporte has always denied intervening in favour of Montpellier but admits he had a telephone conversation with the head of the appeals committee, Jean-Daniel Simonet, before the decision was changed.
Inspectors at the sports ministry established that the committee's decision was "modified" in June 2017.
The appeals committee reduced a fine for Montpellier from 70,000 euros ($82,000) and a match played behind closed doors to 20,000 euros.
Three months earlier, the Altrad group, specialised in construction materials, became the main shirt sponsor of the French national team and threw its financial muscle behind the ultimately successful bid to host the 2023 World Cup.
- 'Important' Altrad -
Another member of the appeals committee, Philippe Peyramaure, said in a defamation trial last year Laporte had called Simonet "and said, in no uncertain terms, that Altrad was a important sponsor for the France team and a key backer for the 2023 bid... and that the punishment had to be removed."
Laporte though said in an interview with newspaper Le Parisien he had merely wanted to "enlighten" Simonet about the tensions in French rugby at that time.
When the weekly publication Journal du Dimanche revealed the existence of Laporte's alleged intervention in 2017, the newspaper also reported a company he owns, BL Communication, had signed an image rights contract with the Altrad Group.
Laporte eventually pulled out of the 150,000-euro deal.
Laporte's questioning comes just two weeks before he faces a bid to regain the presidency against, Florian Grill, and risks disrupting the final stage of his re-election campaign.
Victory for Laporte, who was first elected FFR president in 2016, would leave him in charge of French rugby when the country hosts the World Cup for a second time.
In his club coaching career, Laporte led Parisians Stade Francais and Toulon, guiding the southern club to three straight European Cups.
This year Laporte supported former England captain Bill Beaumont's successful campaign for re-election as head of World Rugby and was rewarded with the vice-president's job.