The US publisher of Harry Potter and the Deathly Hallows is taking legal action against two companies for dispatching copies of the book early.
JK Rowling has hit out at US newspapers that have published plot details from the final Harry Potter book.
Scholastic sued online retailer DeepDiscount.com for breaking the strict embargo of 21 July.
The author said she was "staggered" that papers including The New York Times had printed reviews ahead of the novel's publication on 21 July.
In court papers filed in Illinois, the publisher also named its distributor Levy Entertainment for failing to ensure books were not sent out.
The author said the information was in "complete disregard of the wishes of literally millions of readers".
It said only a tiny fraction of its 12 million copies had been distributed.
UK publishers Bloomsbury said spoilers remained "unauthenticated". Some books have been sent out early in the US.
"The number of copies shipped is around one one-hundredth of one per cent," said Scholastic in a statement.
The book's US publisher Scholastic has sued online retailer DeepDiscount.com for breaking the strict embargo by dispatching a number of copies.
'Please ignore'
The book's contents have been the subject of intense speculationThe novel has also appeared on auction site eBay, while pictures of what appeared to be pages from the new book have appeared on the internet.
The company added that they had a list of customers who had ordered the book from DeepDiscount.com and were asking them to put it to one side if they have already received it by mistake.
Bloomsbury said it was "dismayed" to learn about the early sales. But internet spoilers had not come from the few copies sold ahead of the official publication, it insisted.
A report in The Baltimore Sun newspaper about a customer who had already received his copy prompted Scholastic to take action.
The strict embargo was being "enforced unflinchingly and without exception" by publishers in 93 countries, the company added.
Scholastic is seeking unspecified damages from the two companies for "complete and flagrant violation of the agreements that they knew were part of the carefully constructed release of this eagerly awaited book".
Rowling said the US newspaper reviews would particularly affect children "who wanted to reach Harry's final destination by themselves, in their own time".
A spokesman for Infinity Resources, who own DeepDiscount.com, said: "We take the situation very seriously and are conducting an internal investigation."
"I am incredibly grateful to all those newspapers, booksellers and others who have chosen not to attempt to spoil Harry's last adventure for fans," she added.
JK Rowling has called on fans to dismiss speculation
Rowling's statement follows an earlier message on her website, in which she said: "Let's all, please, ignore the misinformation popping up on the web and in the press.
Levy Entertainment declined to comment.
Some fans are already queuing outside a central London bookshop"I'd like to ask everyone who calls themselves a Harry Potter fan to help preserve the secrecy of the plot for all those who are looking forward to reading the book at the same time on publication day.
Scholastic has also asked "everyone, especially in the media, to preserve the fun and excitement for fans everywhere".
"In a very short time you will know everything!"
Harry Potter author JK Rowling has also posted an appeal on her official website, stating: "Let's all, please, ignore the misinformation popping up on the web and in the press.
On Wednesday, the Baltimore Sun printed a review of the book, saying it had obtained a copy from a relative of one of its reporters who had received it prematurely.
"I'd like to ask everyone who calls themselves a Harry Potter fan to help preserve the secrecy of the plot for all those who are looking forward to reading the book at the same time on publication day.
The New York Times did not say where its copy had come from.
"In a very short time you will know everything!" the statement concluded.
A person selling a copy on eBay said: "I don't work for a bookstore and I don't have a magic wand. An online store shipped a copy early."
'No magic wand'
On Wednesday the Baltimore Sun printed a review of the book, saying it had obtained a copy from a relative of one of its reporters who had received it prematurely.
It says Rowling's seventh book "lacks much of the charm and humour that distinguished the earlier novels" but makes up for it with "hard-won wisdom".
Some fans are already queuing outside a central London bookshopOn the same day, another copy was being offered for sale on internet auction site eBay by a seller who claimed to have received a copy ahead of the release date.
"I don't work for a bookstore and I don't have a magic wand," the seller wrote. "An online store shipped a copy early."
Earlier this week, pictures of what appeared to be pages from the new novel were circulating on the internet.
Minna Fry, marketing director of the book's UK publisher Bloomsbury said: "There have been so many fake books going up on the internet over the past four to six weeks. We have no reason to believe that these are anything other than fake either."
Scholastic issued a subpoena on Monday to California-based social networking site Gaia Online in connection to user-posted material on the book.
In a statement, the website said the link had been immediately removed and that the user in question had been banned for 14 days.
Scholastic also ordered photo-sharing service Photobucket to remove Potter-related material from its site.
Have you grown up with Harry Potter? How old were you when you started reading the books? Will you be waiting in line outside your local bookshop for the final instalment?
Have you grown up with Harry Potter? How old were you when you started reading the books? Will you be waiting in line outside your local bookshop for the final instalment?
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