Goodbye, Big Five, and hello, Big Four.

Penguin Random House has made a deal to buy Simon and Schuster, the New York Times reports, in a move that will rearrange the publishing industry in a big way.

With the sale, Penguin Random House will become a publishing powerhouse. It’s already the country’s largest book publisher, and its acquisition of Simon and Schuster will increase its footprint in the industry exponentially. It will compete in a market with the three other major book publishers, Macmillan, Hachette Book Group, and HarperCollins.

On Twitter, several authors and other literary observers reacted to the news with dismay, many noting that the deal could run afoul of antitrust regulations.

“Well, this is likely a very terrible idea,” tweeted author John Scalzi, whose books are published by Macmillan imprint Tor.

“This merger is obviously illegal,” wrote Matt Stoller. “Random House editors and Simon and Schuster editors bid against each other for books. Now they won’t. Straight up pressing down author wages.” Stoller’s biography at the Federalist Society notes that he’s writing a book about 20th-century monopolies for Simon and Schuster.

And author Tobias S. Buckell tweeted, “Good grief, this can’t be healthy for the book ecosystem in the long run, there’ll just be one company.”

Michael Schaub is a Texas-based journalist and regular contributor to NPR.