According to EDR, the case was brought by De Lotto, the state-owned national lottery, under the Dutch Gambling Act because the companies are not licensed to offer on-line gambling in the Netherlands.
Sites affected are based in the Dutch Antilles, Canada, Antigua, Venezuela, Belize, Haiti and Costa Rica. The Financial Times reports that a total of 40 companies had been called to court with De Loto asking that another 42 companies have said they will take steps to exclude Dutch visitors.
The companies risk fines of €10,000 per day for as long as they continue to deliver on-line gambling in the Netherlands, up to a maximum of €200,000.
The ruling (in Dutch) is here