The delivery drivers weren't aware of the practice due to the lack of transparency. They weren't told how much of the money they get came from tips, so some of them had to experiment by ordering items themselves to figure out what was going on. Going forward, based on Amazon's email, the company will start sending them a fare breakdown for their shift, showing how much their base pay is and how much tips they got.

Here's a photo sample of the breakdown included in the email to drivers:

Here's the full text of the email Amazon sent to contractors: "We are excited to announce that starting August 22 we will be raising Amazon's minimum contribution for Prime Now, Amazon Fresh, and Whole Foods Market blocks. Amazon's contribution will be at least $15-$19 per scheduled hour, depending on location. As always, for deliveries with tipping opportunities, drivers receive 100% of the tips. While earnings vary by region and block, with the change to Amazon's minimum contribution, we expect nationwide average earnings for these blocks to increase to more than $27 per hour."

"While earnings vary by region and block, with the change to Amazon's minimum contribution, we expect nationwide average earnings for these blocks to increase to more than $27 per hour," the email reportedly read.

Amazon has long been criticized for its lack of driver pay transparency. Back in 2015, a group of Prime Now drivers sued the company, accusing it of withholding tips paid via credit cards. One of the plaintiffs said he had no way of knowing if he was paid right, because he had never seen an accounting of his tips.

DoorDash, another company that's gotten flak for counting tips towards its drivers' base pay, has also changed its tipping policy a month after promising to do so in a win. "Under our new model, every dollar a customer tips will be an extra dollar in their Dasher's pocket," the company's announcement reads. "If you leave a $3 tip on your order, your Dasher will earn an extra $3."

Update, 8/23/19 11:00AM ET: This story was updated to include confirmation and a statement from Amazon.