The short, perhaps reductive, version is this: Not satisfied with the cut of the sales price that they get as a bookseller, Amazon wants to force small presses to use their print-on-demand service. They're pressuring the small presses to get in line by saying that they will refuse to sell books that have been printed through any other print-on-demand service. The biggest reason this is a problem is that the one big distribution company that handles almost all distribution to brick-and-mortar bookstores, Ingram, also has a print-on-demand service, and if the small presses don't use Ingram's service, Ingram won't distribute their books. Using both services is prohibitively expensive for small presses, but neither can those presses afford to be forced to choose between bookstores and the Internet.
If the situation is, in fact, as described in the two articles in the above links, then Amazon's plan is bad for small presses, which are perpetually imperiled by distribution costs at the best of times, bad for authors, to whom some small presses would have to pass on the costs of getting their books out through both Ingram and Amazon, and bad for readers, who would encounter obstacles to their efforts to buy books from small presses.
(Full disclosure: Yes, it would specifically be bad for me, because it would make it harder for my publisher to put out a print volume of Rugosa stories.)
If you find Amazon's behavior objectionable, you can contact the Federal Trade Commission to complain. The FTC is in the process of deciding whether to investigate the matter. The number for their complaint line is 1-877-FTC-HELP (1-877-382-4357).
The FTC website offers these instructions for other ways of contacting them about anti-trust issues:
Contact the FTC's Bureau of Competition, and please include your day-time telephone number.
* Phone: (202) 326-3300
* Mail: Write to:
Office of Policy and Coordination
Bureau of Competition
Federal Trade Commission
600 Pennsylvania Avenue, NW
Washington, DC 20580
* Email: email@example.com (Note: Email is not secure. Mark confidential information "Confidential" and send it via postal mail.)