More than 300,000 people have signed a petition urging Apple not to ditch the headphone socket from the version of the iPhone due for release this autumn.
Online reports suggest Apple plans to omit the 3.5mm socket to make the iPhone 7 thinner and more waterproof, with more room for the battery.
The Fast Company reported it would rely on the Lightning cable port, currently used for charging, for sound output.
Others suggest Apple will ship the iPhone 7 with wireless headphones.
SumofUs, a website "fighting for people over profits", which organised the petition, said: "Not only will this force iPhone users to dole out additional cash to replace their hi-fi headphones, it will singlehandedly create mountains of electronic waste that likely won't get recycled."
Tech website The Verge said: "Removing [the] headphone [socket] from phones is something that no-one is asking for and has serious drawbacks including poor compatibility and accessibility, [and] DRM [digital rights management] audio [ie with built-in copyright enforcement]."
Many complained on Twitter that removing the socket would render expensive headphones useless.
Some complained having to use the Lightning port would mean "no music while charging".
One tweeted: "I am OK with Apple removing the headphone [socket] as long as they bundle Lightning EarBuds with the iPhone 7."
Others said that they would not be upgrading.
But not everyone is convinced that losing the jack is a bad idea.
John Gruber, who writes the technology blog Daring Fireball and is regarded as an authority on all things Apple, makes the point that losing the jack would make more room for a larger battery.
"Removing the analogue headphone jack is inevitable. This is what makes Apple different. They will initiate a painful transition for a long-term gain," he writes.
"In five years we'll look at analogue headphone jacks the way we look at all the other legacy ports we've abandoned."
Apple introduced support for headphones over its Lightning cable in 2014.
In the same year, it paid $3bn (£2bn) for the acquisition of headphone maker Beats.
And the Mac Rumours website suggests Apple could be preparing bespoke headphones for the phone.
It noted that a trademark application had been filed for the term "AirPods" in October last year.
And while Apple was not directly linked to these applications, the site said, "the pattern of filings is consistent with Apple's usual strategy".
If the rumours prove true, it will not be the first time Apple has abandoned what it sees as outdated technology.
In 1998 it released the iMac G3 without a floppy disk, leaving many questioning the wisdom of the move.
But, just more than a decade later, Sony - a pioneer of the floppy disk - announced it was killing off the storage device.