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 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.

The move also is a competitive weapon against Apple rival Google Inc., which makes more money from Internet advertising than any other company in the world.

Making ad blockers available on iOS, one of two main smartphone-operating systems, is expected to prompt more consumers to use the technology. The benefits of blocking ads arguably are greater on smartphones than on personal computers, because they can reduce the clutter on small screens and help pages load faster.