MENLO PARK (CBS SF) – Facebook CEO Mark Zuckerberg is criticizing employees for defacing messages supporting the Black Lives Matter movement at company headquarters.

Employees can scribble on walls at the company’s offices in Menlo Park. But in several instances, some workers scratched out “Black Lives Matter” phrases and wrote “All Lives Matter.”

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In an internal memo to employees first obtained by Gizmodo, Zuckerberg wrote in part, “I was already very disappointed by this disrespectful behavior before, but after my communication I now consider this malicious as well.”

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The company is encouraging employees to attend a town hall meeting next week addressing the Black Lives Matter movement.

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According to company data as of May 2015, two percent of Facebook’s staff is black.