A class-action lawsuit has been filed accusing Amazon.com Inc of inflating ebook prices in collusion with some publishers.

The class action lawsuit alleges that the e-commerce giant along with the five largest U.S. publishers, collectively called the ‘Big Five’, agreed to price restraints that cause consumers to overpay for eBooks purchased from them through a retail platform other than Amazon.com.

The development comes a day after Connecticut stated it was investigating Amazon for potential anti-competitive behavior in its business selling digital books.

Amazon declined comment.

According to the lawsuit, around 90% of eBooks are sold through Amazon – the largest U.S. eBooks seller.

In 2011, Hagens Berman, a law firm, had filed a similar lawsuit against Apple Inc and the ‘Big Five’ over ebook prices.