The company that publishes books under the Macmillan imprint has agreed to allow discounting of its electronic books as part of a settlement with the U.S. Department of Justice over price-fixing in the fast-growing e-book market.

Penguin Group has become the latest book publisher to reach a settlement with the U.S. Department of Justice in a lawsuit that alleges that Apple and five publishers had conspired to raise e-book prices.

A Seattle law firm has targeted Apple in an e-book price-fixing lawsuit partly because of the company's dominance in smartphone and tablet sales, the firm's managing director said.