Stade Francais players have gone on strike over a planned merger with rival Parisian rugby club Racing 92, the head of the players' union said.
"They're on open-ended strike," Robins Tchale-Watchou said in a text message.
The clubs announced the surprise merger yesterday, saying it would create a new, stronger club that could enjoy a bigger fan base in the French capital.
Star players in the Racing 92 squad include New Zealand World Cup winners Dan Carter and Joe Rokocoko, while Stade Francais feature the likes of French international Pascal Pape and Italian captain Sergio Parisse.
In recent years wealthy businessmen have invested large sums of money into French rugby clubs, allowing them to sign top players from around the world.
Racing is owned by French property billionaire Jacky Lorenzetti, while businessman Thomas Savare is the current club president of Stade Francais.
Most of the players from both clubs voiced their concern over the merger, which is widely seen by local media and rugby pundits as a takeover by Racing of cash-strapped Stade Francais.
The Paris city hall and the French federation also expressed their concern over the merger.
Racing reached the final of Europe's Champions Cup last season while Stade Francais were finallists in 2001 and 2005.
Players and fans strongly disagree with the clubs that the combination will give birth to a top European side.
Stade Francais' Djibril Camara said it was like "you're suddenly being told you're going to live with your neighbours who you hate".
Racing's Henry Chavancy said: "I've been checking but no, it's no April Fool."
Asked about the strike rumours, players' union chief Robins Tchale-Watchou said: "I am meeting with Stade Francais players today, we'll see what comes out of it."
The former Stade Francais player, now at Montpellier, told Reuters: "Whatever the players decide, we will support them 100 per cent. The players are going to fight."
Tchale-Watchou said the presidents of the two clubs owed explanations to the players.
"The way it has been done is disgusting," he said. "This has been done without any consultation with the players, the fans or the institutions. It's total panic."
Jean-Pierre Chivrac, the head of Racing's fans association, said: "It's like being stabbed in the back."
With Stade Francais president Thomas Savare struggling for funds, the project is being seen in local media as a takeover rather than a merger.
It raises tricky financial and contractual questions. As teams are subject to a monthly salary cap, the new club will have to let go of some top talent, leaving players and staff casting around for a new job three months before the end of the season.
"What do we do about those players who signed pre-contracts for next season, those players who have started making arrangements for next season?" said Tchale-Watchou.
Both Stade's Jean Bouin stadium (20,000 seats) and Racing's Yves du Manoir stadium in Colombes (14,000 seats) are rarely full for league games, though the new super-club is expected to play in Racing's brand new U Arena that should be ready by October.
"You won't fill one stadium with two half stadiums. It's not some French can-can, it's rugby. Fans won't go and support another club just like that," said Tchale-Watchou.