The Swiss Football League (SFL) says it is ready to impose "severe" penalties on Basel after hundreds of the club's supporters went on the rampage following Saturday's title decider.
Under SFL rules, Basel could be ordered to pay a fine of up to SFr100,000 ($83,000), be told to play matches behind closed doors, have points docked – or a combination of all three.
Saturday's dramatic finale to the season, which saw Zurich snatch the title from Basel with a goal in the 93rd minute, was immediately followed by some of the most shocking scenes ever witnessed at a sporting event in Switzerland.
Inside Basel's St Jakob Park stadium police had to form a cordon to protect Zurich supporters, as members of the crowd supporting the home side poured onto the pitch attacking Zurich players and staff.
There was chaos outside the ground as hundreds of Basel fans attacked police who responded with tear gas and water cannon. Supporters trying to make their way home were advised to seek shelter back inside the stadium.
At a news conference on Sunday, police said more than 100 people had been injured and 15 taken to hospital. They added that 300-500 supporters were responsible for the violence and 25 had been arrested.
On Monday the Swiss Police Federation issued a statement strongly criticising Basel for failing to control fans. Damage inside the stadium has been estimated at SFr500,000.
Edmond Isoz, director of the SFL, told swissinfo on Monday that the matter would now go before the organisation's disciplinary committee.
"We had inspectors at Saturday's match and they will now compile a report after speaking to the referee, police and club officials," he said. "This is such a serious case that this process will probably take several weeks."
Isoz declined to comment on what penalties the disciplinary committee might impose, but a senior SFL official, who wished to remain anonymous, promised that "the league will take serious action". The behaviour of Zurich fans is also being investigated.
Basel's hooligan element is generally seen as one of the worst in the country. Two years ago they trashed Thun's stadium, causing tens of thousands of francs of damage.
In July last year the club was fined SFr50,000 by the SFL following incidents at a match against Grasshoppers Zurich that saw damage estimated at SFr100,000 to the Hardturm stadium.
According to the SFL, Basel were also fined on several occasions during the 2004/05 season following incidents both at home and away.
Odilo Bürgy, president of the SFL's disciplinary committee, said the club's record would be taken into account when reaching a decision.
"In my opinion we have a real problem in Swiss football and we have to come down harder in future," he told swissinfo.
"This is the first time we have seen scenes like this in Switzerland and the decision, in my opinion, will be a really severe one."
Speaking after Saturday's match, former club captain Murat Yakin echoed the view of many that not enough had been done over the years to rein in Basel's hooligans.
"We have not come down hard enough on these supporters," he told the Sportinformation news service. "A section of the public is playing by its own rules."
Ralph Zloczower, president of the Swiss Football Association, also spoke of "a Basel problem". While Markus Siegler, spokesman for Zurich-based Fifa, world football's governing body, said Basel needed to educate its fans in the spirit of fair play.
The club said in a statement on Sunday that it assumed "moral responsibility" for what had happened and apologised for the conduct of its fans.
Speaking on Swiss-German television on Monday, Basel president Gigi Oeri apologised once again and admitted that the club had not been in complete control of the situation.
"You cannot call these people fans – they are hooligans and we don't want them here any more," she added.
Oeri said she hoped the SFL would not just impose sanctions but also provide support for finding a solution to the hooligan problem.
swissinfo, Adam Beaumont
In March parliament approved revised federal anti-hooliganism legislation ahead of the 2008 European football championships, which are being hosted jointly by Switzerland and Austria.
The measures include a national hooligan database, travel restrictions and banning orders for known troublemakers. They are being opposed by various Swiss fan clubs who are hoping to force a nationwide vote on the issue.
Sport minister Samuel Schmid called on opponents to back down in the wake of Saturday's events. But a spokesman for the referendum committee, Ruben Schönenberger, said the revised law would not have prevented the violence, adding that opponents had no intention of ending their campaign.
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