The publishing world will watch four major publishers very closely for the next few weeks. According to Publishers Marketplace, Simon & Schuster, HarperCollins, Penguin, and Hachette--a quartet dubbed "Agency Four"--could have their buy buttons removed by Amazon (AMZN) if they can't strike an eBook deal.

Here's an excerpt from the subscription-only story: "The indications are that if the Agency Four have not finalized new digital sales agreements with Amazon prior to the launch of Apple's iPad, they could face delisting from direct sale at Amazon, as Macmillan did."

The New York Times has spoken with unnamed publishing executives about the terms of the eBook deal--noting that major publishers are "reluctant" to strike this kind of deal: "Amazon has agreed in principle that the major publishers would be able to set prices in its Kindle store as well. But it is also demanding that they lock into three-year contracts and guarantee that no other competitor will get lower prices or better terms. "

Last month Amazon pulled the buy buttons on all Macmillan titles, making it impossible to buy directly through the online retailer. If you want to follow buy buttons from the Agency Four, we have a handy guide to double-checking after the jump. (Via MobyLives)

Test the buy buttons for the "Agency Four" with these Amazon links...

Simon & Schuster: Courage and Consequence by Karl Rove
HarperCollins: Neon Angel by Cherie Currie and Tony O'Neill
Penguin: The Help by Kathryn Stockett
Abraham Lincoln: Vampire Hunter by Seth Grahame-Smith