Amazon has started sending out credits to customers following a recently finalised legal settlements with five book publishers, which were accused of conspiring with Apple to fix e-book prices in 2012.

The companies, which included Hachette, HarperCollins, Simon & Schuster, Macmillan and Penguin, have agreed to pay millions in damages to several states’ attorneys general and class-action plaintiffs to avoid charges that they had schemed with Apple to increase e-book prices.

Amazon said in a statement that eligible customers, who purchased Kindle books between 01 April 2010 and 21 May 2012, should have received a notification email from Amazon on 25 March 2014.

"Eligible customers do not need to do anything to receive these credits," the online retailer added.

"If you are eligible, we have already calculated your credit and added it to your Amazon account.

"As long as you have credit remaining we will automatically apply it to your next purchase of a Kindle book or a print book sold by Amazon.com, regardless of publisher.

"The credit applied to your purchase will appear in your order summary."

Amazon will also send account credits to customers who purchased e-books from Barnes and Noble, Kobo, and Apple, while e-books purchased from Sony would be offered with checks in the mail.