Apple Inc.’s move to make it easier to block ads on iPhones and iPads is troubling publishers and heightening tensions with its Silicon Valley neighbors.

The next version of Apple’s AAPL, +1.57% mobile-operating system, due out as early as next month, will let users install apps that prevent ads from appearing in its Safari browser. Putting such “ad blockers” within reach of hundreds of millions of iPhone and iPad users threatens to disrupt the $70 billion annual mobile-marketing business, where many publishers and tech firms hope to generate far more revenue from a growing mobile audience. If fewer users see ads, publishers--and other players such as ad networks--will reap less revenue.