Apples latest mobile operating system, iOS 9, has made it dramatically easier for users to block ads within the mobile version of Safari, with many publishers worried that this could prove a massive problem as more people adopt ad blocking technology.

However, publishers arent the only ones who are concerned, with multiple retailers faced with problems that prevent their mobile websites from displaying on phones using the new wave of iOS ad blockers.

According to Fortune, iPhones and iPads that have downloaded ad blocker Crystal, currently the most popular paid app on the iOS App Store, have been unable to fully render the mCommerce sites of many major retailers, including Sears, Walmart and Lululemon.

Many of the websites are able to load home pages correctly, but as soon as users navigate to specific products, the ad blocking tech from the Crystal app interferes with the coding of the website and results in blank pages being loaded, or prevents items from being added to the shopping cart.

Even on websites that are fully functional from a consumer point of view, ad blocking tech can prevent back-end features like customer analytics from functioning, robbing companies of valuable insights into their audience.

“This upcoming holiday season, content blockers are going to cause a lot of problems,” said Chris Mason, CEO of mCommerce platform Branding Brand. “First, the experience for customers will be lessened. Lots of sites will be missing content, have broken links or customers wont be able to add certain items to their shopping carts.

“Theyll probably just think the site is broken, but its really their content blocker. Second, retailers will be data-blind, or at least data-dark. It will really impact their ability to make quick judgements.”

With the introduction of apps like Been Choice on iOS, which promises to block out in-app and native ads, the problems for adblocking consumers shopping on their iPhones and iPads are likely only just beginning, as are the headaches for retailers, developers and marketers.