Clue, a popular app women use to track their periods, has risen to near the top of Apple’s Health and Fitness category.

It could be downhill from here.

Apple plans this month to incorporate some of Clue’s core functionality such as fertility and period prediction into its own health app that comes pre-installed in every iPhone and is free, unlike Clue, which earns money by selling subscriptions and services in its free app.

Clue’s new threat shows how Apple plays a dual role in the app economy: provider of access to independent apps and giant competitor to them.

“It’s a love-hate relationship, of course. You don’t want to annoy the milkman when you only have one milkman,” said Ida Tin, Clue’s CEO. Though Tin believes her Berlin-based company can coexist with Apple, she said it highlights the “skewed power distribution” in the tech industry.

Developers have come to accept that, without warning, Apple can make their work obsolete by announcing a new app or feature that uses or incorporates their ideas.

When Apple made a flashlight part of its operating system in 2013, it rendered instantly redundant myriad apps that offered that functionality. Everything from the iPhone’s included Measure app to its built-in animated emoji were originally apps in the App Store.

Imitation is common in the tech industry. “We have always been shameless about stealing great ideas,” Apple co-founder Steve Jobs once said.

But what makes Apple’s practice different is its access to a trove of data that nobody else has. The App Store, where the original apps were offered and competed for downloads, collects a vast amount of information on which kinds of apps are successful — even monitoring how much time users spend in them. That data is shared widely among leaders at the tech giant and could be used to make strategic decisions on product development, said Phillip Shoemaker, who served as Apple’s director of App Store review from 2009 to 2016.

The imbalance of power could turn into a rare chink in the company’s armor.

In a climate of unprecedented scrutiny of the power of big technology companies, some wonder whether Apple’s creation of apps imitating ones that already exist on its platform could be harming competition and hurting innovation.

Sen. Elizabeth Warren, D-Mass., zeroed in on the App Store earlier this year. “Either they run the platform or they play in the store. They don’t get to do both at the same time,” she told the Verge.