Facebook’s Menlo Park campus is meant to more closely resemble a Disneyland-style town than an office block. But Gizmodo reports that there’s something pernicious looming within the borders: racism.

On the company’s famous signature wall, where all are welcome to sign their names and express themselves, some employees have been writing “black lives matter” in solidarity with the social justice movement. This is not the problem that caused Facebook founder and CEO Mark Zuckerberg to issue a company-wide message, however. He did so in response to repeated incidents of people crossing out “black lives matter” and replacing it with the reactionary slogan “all lives matter.”

Zuckerberg’s memo, reproduced below, was posted to an employees-only Facebook page for sharing company news and events. He alludes to this behavior being a pattern at the company’s headquarters.

Here’s Zuckerberg:

“There have been several recent instances of people crossing out ‘black lives matter’ and writing ‘all lives matter’ on the walls at MPK.

“Despite my clear communication at Q&A last week that this was unacceptable, and messages from several other leaders from across the company, this has happened again. I was already very disappointed by this disrespectful behavior before, but after my communication I now consider this malicious as well.

“There are specific issues affecting the black community in the United States, coming from a history of oppression and racism. ‘Black lives matter’ doesn’t mean other lives don’t — it’s simply asking that the black community also achieves the justice they deserve.

“We’ve never had rules around what people can write on our walls — we expect everybody to treat each other with respect. Regardless of the content or location, crossing out something means silencing speech, or that one person’s speech is more important than another’s. Facebook should be a service and a community where everyone is treated with respect.

“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. I hope and encourage people to participate in the Black@ town hall on 3/4 to educate themselves about what the Black Lives Matter movement is about.”