Scholastic Corp, the American publisher of 'Harry Potter and the Deathly Hallows', is to sue two companies for shipping copies of the book before the strict embargo.
The book is due to be released when the clock strikes 12:01am Saturday in Britain.
The publishers are suing DeepDiscount.com for sending out the copies early.
They are also suing book distributor Levy Home Entertainment for delivering the books to the online retailer and for failing to ensure that the books were not sent out.
Scholastic said that these books were only a small fraction of the 12m copies due to be distributed.
In a statement, they also asked "everyone, especially in the media, to preserve the fun and excitement for fans everywhere".
In a further breach of the embargo, photographs of what is claimed to be pages from the new novel are circulating on the internet.
Minna Fry, marketing director of UK publisher Bloomsbury told BBC: "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."
