Amazon’s biggest shopping day of the year in 2016 wasn’t actually during the winter holiday shopping rush—but in July.

Prime Day, a one-day sale exclusively for members of its Prime subscription shopping service, debuted in 2015 in the same vein as Black Friday to encourage more spending among its core customer base. The tradition is expected to continue this year, but it might not even be limited to just a day but extended to the entire second week of July, based on chatter in a number of Amazon seller forums.

For sellers, Prime Day offers the potential to add more sales in the week from Prime members, who are known to spend more on Amazon than non-Prime members. Prime members spend an average of $1,300 annually with Amazon, compared to about $700 for non-members, according to research firm Consumer Intelligence Research Partners. Amazon…