Mark is unfriending Tim.

Facebook Inc. FB, +2.66% CEO Mark Zuckerberg doesn’t appreciate how Apple’s AAPL, +1.57% CEO Tim Cook has criticized the social network’s business strategy of monetizing user information.

During a recent interview with Vox Media’s Ezra Klein, Zuckerberg described Cook’s published comments as “glib.”

“ You know, I find that argument, that if you’re not paying that somehow we can’t care about you, to be extremely glib. And not at all aligned with the truth.” ” — — Facebook CEO Mark Zuckerberg, in Vox Media interview

“The reality here is that if you want to build a service that helps connect everyone in the world, then there are a lot of people can’t afford to pay,” Zuckerberg added.

Check out: Why the Facebook controversy could be good for Apple

The Facebook founder’s remarks follow those from Cook that emerged from a coming interview with Recode and MSNBC where the head of the iPhone manufacturer suggested that monetizing user information wasn’t an unpalatable business model for Cupertino, Calif.-based Apple:

“The truth is, we could make a ton of money if we monetized our consumer, if our consumer was our product,” Cook said, according to Recode. “We’ve elected not to do that.”

Read: Facebook will become MySpace, says FANG-focused fund manager

The testy exchange between the billionaire titans of tech come amid mounting concerns about digital privacy, which have intensified after Facebook FB, +2.66% admitted last March that user data were improperly obtained by data-analytics firm Cambridge Analytica for President Donald Trump’s 2016 presidential campaign.

In the aftermath of the that disclosure, Facebook has endured one of its roughest stretches of trading since it went public in 2012. The Menlo Park, Calif.-based company lost 9.5% in the first quarter of 2018, a decline that badly underperformed the market and is attributed with helping to fuel a wider selloff in technology focused equities.

The Dow Jones Industrial Average DJIA, +0.51% lost 2.5% in the first three months of the year, the S&P 500 index SPX, +1.05% shed 1.2%, while the technology-centered Nasdaq Composite COMP, +1.71% gained 2.3% in the first quarter of 2018, by comparison. The tech-heavy fund PowerShares QQQ Trust Series 1 QQQ, +1.85% , where Facebook is a major component, also gained 2.8% over the same period.

For Cook’s part, his company’s stock has also underperformed the broader tech market, Apple’s stock has fallen 0.9% year to date.