An employee unloads a truck load of Amazon.com packages at the United Parcel Service (UPS) Chicago Area Consolidation Hub in Hodgkins, Illinois. Daniel Acker | Bloomberg | Getty Images

Amazon is trying to lure business buyers onto its fast-growing marketplace, offering them extended periods to pay for things like heavy equipment and office supplies. Sellers fear the change is coming at their expense. In an email to sellers earlier this month, Amazon said that third-party merchants, which utilize the company's fulfillment centers and logistics system, would be part of a new policy that gives qualified businesses 30 days to pay their bills. For consumer products, sellers are used to getting paid within a week or two. By applying the "Pay by Invoice" service to the broader marketplace, corporate customers no longer have to rely on the specialized Amazon Business to get the benefit of a longer payment period. Starting August 8, products from general marketplace sellers would "automatically become eligible for invoiced purchasing," according to the email, which was viewed by CNBC.

Lengthening the cash payment cycle could create a cash crunch for sellers who rely on speedier payments to buy inventory and fund their operations, said Jerry Kavesh, the CEO of 3P Marketplace Solutions, a consulting firm for Amazon marketplace sellers. "Cash is always tight and challenging for small companies," said Kavesh. "This policy could put sellers in a cash bind, where they may not be able to pay suppliers and employees, which is problematic at best, and worst could put them out of business." An Amazon spokesperson declined to provide a comment for this story.

Sales growth vs. slower payments

Amazon told sellers in the email that the change is meant to draw more corporate buyers to the marketplace, and could open up a new revenue channel from customers who wouldn't otherwise shop with them. Sellers that want the cash faster than 30 days can pay an additional 1.5 percent of the invoiced amount. "Pay by Invoice represents a new growth opportunity for sellers by encouraging Amazon Business customers to use the Amazon Marketplace as their primary channel for B2B purchases," Amazon wrote. But sellers are skeptical. One seller, who asked to have his name withheld out of fear of retribution, said Amazon should have given merchants the choice to participate because cash management is such a sensitive part of their business. Amazon is "using you, the seller, to finance the growth" of its business customers, the seller said.

Amazon first announced plans for the new policy in May, sparking debate across the seller forums as to whether it would be a benefit or hindrance. One merchant wrote, "This might work for big distributors with enough budget to cover any terms, but not for me or any small business owners." Another post said, "Just a single order for $5,000 of gear not paid for 30 days is enough to put many small businesses in a cash flow pinch with their suppliers, who are NOT going to wait 30 days."

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