BlueMail creators Ben and Dan Volach released a letter Tuesday calling for developers to share their complaints about Apple and its power as holder of the iOS platform.

"If Apple has kicked you out of any of its App Stores, used its developer guidelines to control your innovation, hijacked your store ranking, or (let's be honest with each other) lied to you while it steals your technology, it's time to talk," Dan Volach wrote in an open letter posted Tuesday.

Blix, the Volach brothers' company, has been engaged in both a war of words and a legal battle with Apple after BlueMail was removed from the Mac App Store.

The open letter comes not long after companies including Tile testified in front of the US House of Representatives, accusing Apple and others of unfairly privileging its own apps and services in iOS above those of outside developers.

Apple says that the decision to remove BlueMail was based on security concerns and nothing more: "The App Store has a uniform set of guidelines, equally applicable to all developers, that are meant to protect users," it said.

Visit Business Insider's homepage for more stories.

Seven months ago, brothers Dan and Ben Volach — proprietors of Blix, a small software company — took a rare and dramatic step: They opted to take on Apple, suing the company over allegations of patent infringement and anticompetitive behavior.

Now, in the wake of an widely-watched antitrust hearing, where firms like Tile and Sonos accused Apple and Google of quashing competition in front of a United States House of Representatives committee, the Volach brothers are hoping other smaller tech firms will also be willing to air their grievances against Apple.

"If Apple has kicked you out of any of its App Stores, used its developer guidelines to control your innovation, hijacked your store ranking, or (let's be honest with each other) lied to you while it steals your technology, it's time to talk," Dan Volach wrote in an open letter posted Tuesday.

"It's not only about Tile or Sonos or Blix," Ben Volach told Business Insider. "We think there's thousands and thousands of companies out there, that are suffering."

And as the government pays closer attention to developers that are speaking out, the brothers are hoping to recruit allies in their fight against Apple. The goal, "at the end of the day, is to create enough pressure on Apple to change," Volach said.

A brewing battle with Apple

Blix has been locked in conflict with Apple for some time now, butting heads over its email app Bluemail.

The Volach brothers say that Apple imitated Bluemail when it created the new "Sign in with Apple" feature, which enables users to generate a random email address for apps when signing in. Furthermore, the brothers say that Bluemail was kicked off of the Mac App Store for having the feature in question, which they say makes Apple a hypocrite for copying something that it says is a violation of its own terms of service.

In response, Blix has adopted a two-pronged approach: It is suing Apple over allegations of patent infringement and antitrust violations, even as it appeals directly to the tech titan to get Bluemail back onto the Mac App Store. It also more recently accused Apple of manipulating App Store search rankings.

This strategy hasn't had much success so far. The Volach brothers last published an open letter to Tim Cook in November, in a plea to get their app back on the store.

"When we take [our app] to Apple now, there's no higher authority that we can actually approach to show that [the decision] is not according to their own recommendation or based on fact," Ben Volach told Business Insider.

"A productive approach would be for somebody to be outside monitoring this process," he added. "Apple doing it on its own is just not good enough."

Apple, for its part, has pushed back against Blix and its claims. In a statement, Apple notes that Bluemail is available on the iOS App Store, and that Blix has another app already available on the Mac App Store. Furthermore, Apple says, Blix has been unreceptive to the idea of working together.

"We have attempted on multiple occasions to assist them in getting their BlueMail app back on the Mac App Store. They have refused our help," Apple says in its statement.

Apple also says that it's a matter of user security, and nothing more: "The App Store has a uniform set of guidelines, equally applicable to all developers, that are meant to protect users. Blix is proposing to override basic data security protections which can expose users' computers to malware that can harm their Macs and threaten their privacy."

Apple under fire from its own developers

The Volach brothers' allegations — and any additional stories that they manage to get from other developers — only add to a pile of complaints that have steadily been growing against Apple, as the US government ramps up its scrutiny of big tech firms.

Apple's crackdown on parental-control apps like Freedom and Mobicip for violating privacy prompted pushback from its developers, who said that their expulsion from the App Store was to help Apple's own apps. Apple reversed that policy in June, amid reports that the US was stepping up its scrutiny of the iPhone maker.

In September, an analysis from the New York Times found that the App Store packed Search results with Apple's own apps. And even Apple's big music streaming competitor Spotify filed an antitrust complaint with the European Commission in March, alleging that Apple's 30% tax levy on third-party apps, along with other tactics, were quashing competition.

Apple had denied all claims that it quashes competition, and referred Business Insider to its policies and practices page,. The page acknowledges that Apple has "strict guidelines on privacy, design, and business models," and that it has removed 1.4 million apps from the App Store since 2016 for violating those guidelines. But Apple has also stressed that it helps app developers adhere to its guidelines to get back on the store.

Got a tip? Contact this reporter via email at bsapra@businessinsider.com, Telegram at bani_sapra or Twitter DM at @bani_sapra (PR pitches by email only, please).