A group of prominent authors says Amazon.com Inc. has “unprecedented power” over the book publishing market and wants the U.S. Department of Justice to begin an investigation of what it claims is a monopoly.

On Thursday, the Authors United group submitted a formal request to the DOJ’s top antitrust official. The group formed last year in response to Amazon’s bruising negotiations with publisher Hachette Book Group, primarily over pricing.

Led by author Douglas Preston, the group sent a letter to the DOJ that said Amazon has repeatedly blocked or limited the sale of thousands of books on its website, sold some books below cost to gain market share, and attempted to compel customers to buy books from its own imprints rather than from other companies.

“We respectfully request that the Antitrust Division investigate Amazon’s power over the book market, and the ways in which that corporation exercises its power,” Authors United said in its letter, reviewed by The Wall Street Journal. Authors United had been working on its formal appeal to the agency since at least September.

A Justice Department spokesman said the agency will review the group’s materials.