Yahoo has stopped some of its customers accessing their email inbox if they are running ad blockers, in an attempt to dissuade people from using the software.
Customers in the US have reported seeing a message from the internet company asking them to disable their ad blocker before being able to view their inbox.
Although some users said they had been able to circumvent the message, others haven't been so lucky and were disappointed Yahoo was taking such steps. In fact, one customer, Andrei Herasimchuk - Yahoo's former Senior Director of Product Design, said he was planning to move to Apple Mail as a result of Yahoo's actions.
"So @YahooMail has blocked my inbox for using an ad blocker. It was a good run, I guess. Goodbye! Hello Apple Mail, as much as I hate it," he wrote on Twitter.
Yahoo said it had made the move as part of its US product testing scheme, but it didn't say whether it would continue to test the pop-up or disable it as a result of customer complaints.
The company explained only some users were seeing the message because it was A/B testing the ad blocker detecting technology.
"At Yahoo, we are continually developing and testing new product experiences. This is a test we're running for a small number of Yahoo Mail users in the US," a spokesperson told Engadget.
Yahoo is the latest company to restrict access to its website for those running ad blockers. In the past, high-profile companies including The Washington Post and City AM have trialled similar methods to encourage users to disable ad blocking tech.
Tom Yeomans, CEO of Yavli, a company that makes technology to subvert ad blockers, told Digiday: "They're likely testing this particular approach, banning ad blocker users, on their email service because they know their users will be forced to disable their ad blocker if they want to check their emails within their web browser.
"Their users' email account content are unique to them, so it's different from news content where they can visit a competing website to get a same or similar experience."
