“Amazon keeps changing the rules without explanation,” Atkinson said. “I know they’re not a charity, but a small company like ours doesn’t stand a chance.”

James Thomson, a former Amazon managing director who serves as chief strategy officer at marketing consultancy Buy Box Experts, said the tensions between online retail giants and small mask makers reflected the greater debate about the oversized power of online platforms to power the retail landscape dominated. Mr Thomson, whose company helps Marken steer Amazon’s complex sales policy, said his seemingly contradicting approach to N95 masks – claiming such goods are reserved for medical staff, but then allow exemptions for masks they are in bulk bought – is likely a result of Amazon’s loyalty strategy.

“Even if they’re making next to no money on this mask, the real thing is to keep customers happy so they don’t go elsewhere,” said Thomson. “The problem is, if you let these practices scale, it becomes disruptive to everything else that isn’t Amazon.”

It’s hard to overestimate the sales power of tech giants. Max Bock-Aronson, co-founder of Breathe99, a Minnesota start-up whose washable face mask filters out 99.6 percent of microscopic particles, said his company has been sick since Facebook dropped its ads in December, causing a decline of 50 percent resulted in sales. “Due to our cash flow crisis, we can only produce small quantities of masks, but these are sold out immediately,” said Bock-Aronson.

He is particularly annoyed by the company’s claims of having to protect the public as Facebook is unwilling to combat misinformation regarding political and pandemic-related content on its platforms.

“It’s just frustrating because we’re waving our hands and saying, ‘Hey, we have a better mask that can protect people,’ but we’re really not allowed to talk about it on their website,” he said. “It’s hard enough to start a business in normal times, but it’s nigh on impossible with those businesses excluding you from the market.”

In statements, Facebook, Google and Amazon said they had no immediate plans to revise their guidelines.