Consumer advocates and small businesses are crying foul over an Apple software upgrade that's shutting down some iPhones after people get them fixed at third-party repair shops. 

It's called "Error 53" and it's happening to iPhone 6 and 6s users who bring their devices to non-Apple technicians for repairs. 

"It's a widespread issue," Trent Forrest, owner of the Palmedic wireless repair shop in downtown Ottawa, told CBC News. "I feel something should be done."

Not all repairs trigger the problem. Getting your screen replaced at a mom-and-pop shop likely won't cause any trouble. But anything involving the device's home button could render your phone useless. 

And it appears to be specifically tied to the most recent iPhone software upgrade. In some cases, a person's phone may function properly after a repair until the moment they install iOS 9.

According to a report by the U.K.'s Guardian newspaper, Error 53 has affected thousands of people.

Apple says it's a security feature, meant to prevent fraudulent activity on phones that have fingerprint Touch ID. 

"We take customer security very seriously and Error 53 is the result of security checks designed to protect our customers," Apple Canada said in an e-mailed statement to CBC news.

"iOS checks that the Touch ID sensor in your iPhone or iPad correctly matches your device's other components. If iOS finds a mismatch, the check fails and Touch ID, including for Apple Pay use, is disabled. This security measure is necessary to protect your device and prevent a fraudulent Touch ID sensor from being used. If a customer encounters Error 53, we encourage them to contact Apple Support."

Possible class-action 

If it's a security feature, then it goes too far, says Canadian consumer advocate David Fewer.

If Apple is worried about fraudulent activity, it would make more sense to temporarily disable pay features on the phone than shut it down altogether, he told CBC News.

"Why on Earth would you disable my ability to place a phone call with a service I pay for on a device that I own?" Fewer, director of the Canadian Internet Policy & Public Interest Clinic at the University if Ottawa, said.  "This is by far the most Draconian security measure that we've seen."

What's more, he said, it stifles competition, forcing customers to choose Apple over a local repair shop, even if the latter is closer and cheaper.

Forrest told CBC News his repair shop turns away costumers looking for any fixes that could trigger Error 53.

"This has already had a competitive impact that's going to boost Apple's profits," Fewer said. "All of a sudden, it just got that much more expensive to own an iPhone."

He called it "class-action material," and at least one U.S. law firm agrees. 

Seattle-based PVCA agrees issued a call on its website for people affected by Error 53 to join a class-action lawsuit against Apple. 

"Think of it this way: Let's say you bought a car, and had your alternator replaced by a local mechanic. Under Apple's strategy, your car would no longer start because you didn't bring it to an official dealership. They intentionally disable your car because you tried to fix it yourself," PVCA says.