Mark Zuckerberg, chief executive officer and founder of Facebook Inc. attends the Viva Tech start-up and technology gathering at Parc des Expositions Porte de Versailles on May 24, 2018 in Paris, France.

Facebook CEO Mark Zuckerberg isn't as overwhelmingly popular among his employees as he once was, recently released Glassdoor data shows.

Zuckerberg fell 39 spots in Glassdoor's annual ranking of top CEOs for its Employees' Choice Awards, from No. 16 to No. 55, falling out of the top 20 for the first time since Glassdoor kicked off the survey in 2013.

His employee approval rating remains high, at 94%, according to Glassdoor, but is down from 96% last year. Zuckerberg came in first place in Glassdoor's first iteration of the ranking in 2013.

The drop in his ranking may reflect internal unease as the company has juggled various publicity crises over the past year. Multiple former Facebook recruiters told CNBC that Facebook has had a harder time recruiting talented new hires since the March 2018 Cambridge Analytica scandal, in which a political research firm improperly accessed user data to target political ads meant to help President Donald Trump in the 2016 election.

Facebook's stock price is also near the same level it was in January 2018, which may also have hurt the rankings, as many employees receive stock as part of their compensation.

Zuckerberg lagged behind tech peers such as Google CEO Sundar Pichai, who also received a 94% CEO approval rating but came in 46th place overall.

But Zuckerberg still came ahead of Apple CEO Tim Cook, whose approval rating was 92%, landing him in the 69th spot on the list.

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