A US court has threatened to shut down the Spamhaus Project, a volunteer-run antispam service, for ignoring an $11.7m (about £6.3m) judgement against it.

In a proposed court order, Judge Charles Kocoras of the US District Court for the Northern District of Illinois calls on the organisations responsible for registering the Spamhaus.org internet address to suspend their internet service. Both Icann (the Internet Corporation for Assigned Names and Numbers) and Tucows, the Spamhaus.org registrar, are named in the order.

The proposed order follows a 13 September ruling in which Spamhaus was required to pay damages and stop listing an email marketing company called E360Insight LLC in its database of known spammers. Spamhaus, based in London, has said it ignored the judgment because it cannot be enforced in the UK.

Matthew Prince, CEO of Unspam Technologies and an adjunct professor of law with the John Marshall Law School, said that although the order is not yet final and may be part of "the judge's gambit to get Spamhaus to come back to the table", there's nothing to prevent it from being finalised.

"In other words, there may be some time before Icann is formally ordered to shut down the Spamhaus domain, but make no mistake... Icann's lawyers will be considering their options," he wrote in a blog.

Shutting down Spamhaus is certainly a possibility, according to Prince. "I don't know what Icann will do, but I bet they'll at least consider complying," he wrote.

If Icann does shut Spamhaus down, it could be bad news for email users. Spam now makes up about 90 percent of all email and Spamhaus reckons it helps block between 8 billion and 10 billion of these messages per day.

Spamhaus' spammer blacklist is used by several technology vendors including Microsoft.

Spamhaus could not be reached for comment, but it has said it intends to appeal the ruling. "The Illinois ruling shows that US courts can be bamboozled by spammers with ease, and that no proof is required in order to obtain judgments over clearly foreign entities," Spamhaus said in a note on its website.

"Spamhaus is, however, concerned at how far a US court will go before asking itself if it has jurisdiction, and is intending to appeal against the ruling in order to stamp out further attempts by spammers to abuse the US court system in this way."