Apple's latest update for iPhones and iPads, iOS 9, makes it easier to block ads in the mobile version of Safari.
That sounds like a great thing for consumers who get to view their favorite websites without getting interrupted by pesky ads.
But it actually presents a big problem for companies that make most of their money from mobile ads — like most media companies.
As it turns out, installing these ad blockers has also caused a significant problem for e-commerce websites, which Fortune's Dan Primack first reported. Installing an ad blocker such as Crystal — which is currently the top paid iOS app — could affect the way shopping websites are displayed.
For instance, Sears.com was unable to load when Primack viewed it with the Crystal ad-blocking app installed. Outdoor equipment shop Bass Pro Shops was unable to display the image of a product when Primack tried to view it. While the homepage for Walgreens worked, Primack said he couldn't add anything to his cart.
I experienced a similar issue when enabling Crystal while using Safari. An entire product page on Walgreens.com disappeared when I turned on the extension.
Here's how it looked when Crystal was turned off:
And here's what happened when I turned it on:
Tom Caporaso, the CEO of Clarus Commerce which operates FreeShipping.com, sees this as a problem for online retailers.
"It's something you definitely have to be worried about, especially at this time of year," he said to Business Insider.
Apple could not immediately be reached for comment about the ad-blocking apps' impact on e-commerce sites.
Do the math
Caporaso noted that 30% of all e-commerce transactions now happen on mobile devices, with lines up with findings from display marketing firm Criteo.
"As you do the math, it gets very large very quick," he said.
Most retailers tend to shut down technical work in mid November to ramp up for the holiday shopping season, which means they may have a limited amount of time to work around this.
"Any kind of recoding or technical work that they need to make has to happen very quickly," he said.
But there's a problem other than ad blockers potentially impacting e-commerce transactions. E-commerce sites, like most other websites, also rely on display advertising. If a significant group of consumers block third-party ads on these sites from view, it could mean trouble.
"Those [ads] are blocked, and those [ads] don't get revenue," he said. "That's going to have a dramatic impact on their core business."
Caporaso thinks that as ad blockers grow in popularity, online retailers will have to learn how to tailor their platforms to work correctly even while these extensions are turned on.
"It will be very hard to sway customers not to put [ad blockers] on their phones if that's what they want to do," he said. "...I think the more velocity these ad blockers get, the more resources these retailers will put toward trying to figure out and fix it."
