Facebook CEO Mark Zuckerberg furiously reprimanded employees in a private memo on Thursday, warning them to "stop crossing out 'black lives matter' and writing 'all lives matter'" on the company's famous signature wall in Menlo Park, California, calling such behavior "disrespectful" and "malicious."
"Black lives matter doesn't mean other lives don't," Zuckerberg wrote in the scathing message, posted on an internal forum and obtained by Gizmodo. "This has been a deeply hurtful and tiresome experience for the black community and really the entire Facebook community, and we are now investigating the current incidents," he added.
Employees have always been encouraged to write or draw on the whiteboard walls at Facebook -- essentially a real-life version of Facebook's virtual timeline wall. "We've never had rules around what people can write on our walls," wrote a seething Zuckerberg, "We expect everybody to treat each other with respect."
The Black Lives Matter movement started when George Zimmerman was acquitted in the murder of Trayvon Martin, and has since become a nationwide protest about police brutality against African Americans.
Facebook has drawn criticism in the past for its WASPy, frat-house culture, and suffers from a lack of diversity — only 2 percent of employees are black.
This story originally appeared on NBCNews.com.