A Wayfair employee works at his desk at the Boston headquarters of Wayfair on July 31, 2018.

Dave Kerpen was hoping prices would drop on some expensive tickets for a late-September New York Mets game. He kept checking the prices to no avail.

At one point, he checked his StubHub app and added the tickets to his cart. He decided not to buy just then, and closed the app.

Almost right away, he got a phone call. It was StubHub, telling him he could get a 5% discount for the tickets if he bought them immediately over the phone.

"It was surprising because I didn't even realize they had my phone number," Kerpen, an author and entrepreneur, told CNBC. "If it startled me, it probably startled most people."

Creepiness aside, Kerpens said he was disappointed in the meek 5% discount offer and didn't buy the tickets, but added "it probably works part of the time or they wouldn't be doing it."

A StubHub spokeswoman said the company began doing this more than three years ago "for select events" to help consumers with factors like the best seat or the best day to attend an event. She said the practice is to first reach out by email then follow up by phone. Kerpen said he had not received an email.

"When consumers are considering a high cost purchase, there is a desire for a more personal touch, which can give them greater confidence," StubHub wrote in an emailed statement.

It's not surprising that a big internet company — StubHub is owned by eBay — would track consumer activity on the web. That's how brands target users with such increasing precision and how data collection firms build comprehensive profiles that can help advertisers get the messages to the right people at the right time.

But after several years of high-profile scandals over how big internet companies like Facebook collect and use data from users, consumers are paying a lot more attention — especially if they're not sure how a website got their number.

Last week, comedy writer Ariel Dumas wrote on Twitter that she received a phone call from furniture retailer Wayfair while browsing its website. She wasn't happy about it.

https://twitter.com/ArielDumas/status/1190053718252756993?s=20

A Wayfair spokeswoman told CNBC in an emailed statement that the company recently started testing outbound calls to less than 1% of customers "to assist them in the shopping process."

"We do not make any outbound phone calls based on real-time site activity," the representative said. "In all cases, customers receive an introductory email from the team prior to any phone outreach."

Critics have also taken to Twitter to criticize T-Mobile, ePromos, Staples and Liberty Mutual for what they claim is similar behavior. ePromos and Staples didn't respond to a request for comment. Liberty Mutual did not provide a comment as of press time. T-Mobile declined to comment on the record.

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