The creators of several Virtual Private Networks (VPNs) have criticised Apple's decision to remove their products from its App Store in China.
The BBC understands that as many as 60 VPNs were pulled over the weekend.
Apple said it was legally required to remove them because they did not comply with new regulations.
It refused to confirm the exact number of apps withdrawn, but did not deny the figure. It added that dozens of legal VPN apps were still available.
VPNs allow users to hide IP addresses and access online material that might be blocked by internet filters.
Which VPNs have been affected?
A company that analyses mobile app sales, www.aso100.com, has told the BBC that more than 60 VPNs were no longer available in Apple's China mainland App Store.
Golden Frog, the company that distributes VyprVPN was critical of the decision, saying it would file an appeal with Apple.
"If Apple views accessibility as a human right, we would hope Apple will likewise recognize internet access as a human right (the UN has even ruled it as such) and would choose human rights over profits," said Golden Frog's president Sunday Yokubaitis in a blog post.
ExpressVPN said it was "dismayed" that the tech giant had "sided with censorship."
The apps are still available in Apple's App Stores outside China.
Who uses VPNs in China and why?
China has for many years censored content it sees as politically sensitive, using an increasingly sophisticated set of filters that critics have called the "great firewall."
In its most recent rankings, the advocacy group Freedom House dubbed China "the year's worst abuser of internet freedom."
VPNs allow users to skirt around these filters and gain access to websites and services that are restricted or banned.
There is no outright ban on VPNs, and in fact many major corporations use them legitimately under the current laws.
The latest push to tighten access has targeted VPNs that are mostly used by individuals rather than companies.
Why did Apple remove the VPNs?
In January, China's Ministry of Industry and Information Technology announced that all developers offering VPNs must obtain a license from the government.
And Apple said it was required to remove some VPN apps from its store because they didn't comply with those regulations.
But it is fair to say that Apple has many reasons to be wary of incurring Beijing's wrath.
The tech giant makes much of its hardware in China, and it has become a major market for its products too.
And with low cost local competitors cutting into the iPhone's market share, Apple's profits are more likely to depend on apps and services, some of which could run into China's censorship regime.
Earlier this month Apple also established its first data centre in China, in conjunction with a local company Guizhou-Cloud Big Data Industry.
Although Apple said it would retain the encryption keys and would not compromise users' privacy, some experts have suggested that housing data in China could create pressure for Apple to hand over data in future disputes.