An East Coast seller, who asked that we not use his name for fear of retribution from Amazon, said he’s been selling books on the site for 13 years, generating over $1 million in gross revenue, and this is the first time he’s been forced to alter his delivery time. He expects his shipping costs to increase by 25 percent to 50 percent because he will no longer be able to rely on the U.S. Postal Service for cross-country deliveries and will instead have to use a more expensive express option.

Amazon didn’t respond to a request for comment.

The USPS has a special rate for media items and says on its website that delivery times range from two to eight days. But sellers told CNBC that coast-to-coast shipments often take a few days longer than that. The risk to missing Amazon’s guaranteed delivery window is that a seller gets bad reviews, which means losing visibility on listings and can eventually lead to suspension.

It’s been a rough year for media sellers on Amazon.

In March the company increased fees that those merchants pay for each item to $1.80 from $1.35. Then, as part of its crackdown on counterfeits, Amazon forced sellers of certain textbooks to show invoices before listing their items. Merchants buying used items from places like garage sales were suddenly stuck with unsellable inventory.

“Over the last six to eight months, there’s been a string of things coming out and it seems to be getting harder and harder in media,” said Tedric Paulk, co-founder of Oaxray, which helps sellers find inventory for their Amazon business. “They’re just trying to increase customer experience, and if it gets rid of some media sellers, I don’t think they’re worried about that.”

Books and music are already a tough market for Amazon merchants. Media has long been going digital, and Amazon is encouraging the move through Kindle and devices like the Fire TV Stick and Echo. Additionally, Amazon is opening its own physical book stores.

Now sellers have to find another way to make up for rising costs, and they have only a few short weeks to do so.

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