Jessica Guynn

USA TODAY

SAN FRANCISCO — Facebook CEO Mark Zuckerberg is responding forcefully after incidents in which employees crossed out "Black Lives Matter" and wrote "All Lives Matter" on the walls of the company's Menlo Park, Calif., campus.

Facebook, whose staff is 2% black, is investigating the racially charged incidents in which the movement's slogan was defaced. Those actions have been a "deeply hurtful and tiresome experience for the black community," Zuckerberg said in an internal post obtained by Gizmodo.

Facebook declined to comment.

POLICING THE USA:A look at race, justice, media

"We've never had rules around what people can write on our walls," said Zuckerberg in the post. "We expect everybody to treat each other with respect."

It's a longstanding tradition at Facebook that employees can write on the walls, dry-erase message boards or chalkboards, much as they would on their virtual wall on Facebook.

"There have been several recent instances of people crossing out 'black lives matter' and writing 'all lives matter' on the walls" Zuckerberg wrote. "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."

Zuckerberg encouraged Facebook employees to attend a town hall next week "to educate themselves about what the Black Lives Matter movement is about."

Black Lives Matter began as a hashtag on Facebook after the acquittal of George Zimmerman in the killing of Trayvon Martin, an unarmed black teen, and became an Internet-wide protest slogan after the police slayings of African Americans.

Today it's a civil rights movement that has taken on a national role in demanding an end to police brutality and mass incarceration. African American leaders, including President Barack Obama, have said the Black Lives Matter's name shouldn't be construed as suggesting no one else's live matter, but to point out a specific problem happening in African American communities. But some politicians and groups, including police supporters who oppose the movement, have rallied behind the #AllLivesMatter hashtag.

A fraction of the tech work force in Silicon Valley is African American and little progress has been made on the problem. Only 1% of venture-capital-backed start-ups are led by African-Americans and less than 1% of general partners at major venture capital firms in Silicon Valley, the ones that back tomorrow's Facebooks and Googles, are African American.

The predominantly white male industry runs the risk of losing touch with the diverse nation — and world — that forms its customer base. At the same time African Americans are being excluded from the fastest-growing, highest-paying jobs in the nation.

Follow USA TODAY senior technology writer Jessica Guynn @jguynn