Facebook CEO Mark Zuckerberg had a few sharp words for some of his employees after discovering that they have been crossing out “Black Lives Matter” on the doodle boards of the Menlo Park headquarters and replacing them with “All Lives Matter.”

Mark Zuckerberg called out Facebook employees for crossing out Black Lives Matter slogans: https://t.co/Mzlrq2VxAb pic.twitter.com/xdRZj8XCDR

— Forbes Tech News (@ForbesTech) February 28, 2016

Tech blog Gizmodo was able to acquire an internal memo penned by Zuckerberg and posted on a company-wide announcement page. In the memo, the 31-year-old mogul admonished staff members for defacing the slogans and described the acts as “malicious” and unacceptable. He also reminded them that he had already given prior warning during a Q&A session held the previous week.

Facebook is known to encourage its more than 12,000 employees to write freely and express themselves on the huge chalkboards, dry-erase boards, and walls found around the main office, emulating the virtual “wall” that the social media giant has made so popular.

Mark Zuckerberg blasted his own staff for defacing #BlackLivesMatter notes at Facebook’s headquarters https://t.co/femaE0egh5

— Newsweek (@Newsweek) February 27, 2016

However, Mark Zuckerberg emphasized the importance of respecting each other’s views and opinions.

“We’ve never had rules around what people can write on our walls,” stated Zuckerberg in the post. “We expect everybody to treat each other with respect.”

“I was already very disappointed by this disrespectful behavior before, but after my communication I now consider this malicious as well,” he added.

Mark Zuckerberg may seem adamant in fostering an atmosphere of diversity and equality within his company, but statistics show that only about 2% of Facebook’s workforce consists of African Americans. Other well-known companies in Silicon Valley are not that different, and the progress in hiring more non-white employees has been quite slow.

Here is a breakdown of Facebook’s U.S. diversity stats: https://t.co/3aStavcBQ1 pic.twitter.com/bcgnnr9opU

— Forbes (@Forbes) February 25, 2016

“Black Lives Matter” actually started out as a hashtag on Facebook in 2013 following the acquittal of George Zimmerman, a white/hispanic man who gunned down an unarmed black teen named Trayvon Martin.

Facebook is currently investigating the defacement incident and is also scheduled to hold a 30-minute town hall on March 4^th. Mark Zuckerberg invited his employees to attend the meeting, which aims to educate and enlighten them regarding the Black Lives Matter movement.