French ISPs have been told to block the site, stanjames,com, for two months. Any that do not will pay a penalty of €10,000 a day, the Tribunal de Grande Instance in Paris ruled. The ruling is the result of an injunction request from French gambling regulator Arjel.
Head of the French telecoms federation Yves Le Mouël told AFP that the court's attention should have focused on the operator of the site and its host, not on ISPs. "The blocking of a site is always very difficult," he said, according to an automatic translation.
Le Mouël said that the court had imposed the requirement on ISPs because it was easier than taking action against the Gibraltar-based operator or its UK-based host.
The court ruling also imposed an obligation on ISPs to screen certain messages to ensure that users were not circumventing any measures ISPs put in place, AFP said.
"Screening is the wrong solution, and opens the door to a generalisation of that practice," Le Mouël told the agency. "We are like the postal service, we do not open the mail."
Pressure group Right2Bet, which campaigns for the liberalisation of gambling laws and is backed by gambling firms including Stanley and BetFair, said that the ruling is unfair.
"The ruling is another kick in the teeth for French consumers still fuming from the recent legislation which has failed to provide them with an open and fully competitive gambling market," said a blog post by the organisation.
"The idea that in this day and age, a leading country like France can begin censoring the internet is difficult to comprehend, yet such is the desire of Arjel and others to protect local providers, the PMU and FDJ, that these backwards measures are a reality," it said.
Online gambling has proved legally controversial across Europe, as increased access to gambling operators has clashed with laws in many EU countries, which often restrict gambling to a state-controlled or state-licensed monopoly.
A ruling from France's highest court in 2007 established that France could not maintain its gambling monopoly because it conflicted with EU competition laws.
The European Court of Justice ruled that Sweden is permitted to bar foreign gambling companies from operating without a licence there, but only if the same rules and penalties apply to domestic unlicensed operators.
The Court said that Sweden's laws were a restriction on traders and consumers that would usually be unlawful, but that EU law allowed such restrictions on the grounds of public policy, security or health.
"The legislation on gambling is one of the areas in which there are significant moral, religious and cultural differences between the Member States," that ruling said. "In the absence of Community harmonisation in the field, it is for each Member State to determine in those areas, in accordance with its own scale of values, what is required to protect the interests in question."