Mark Luckie, who is black, said Facebook's population of black employees is not representative of its black user base.
"There is often more diversity in Keynote presentations than the teams who present them," Luckie wrote in the note, which he originally shared with Facebook employees on Nov. 8.
"In some buildings, there are more 'Black Lives Matter' posters than there are actual black people. Facebook can't claim that it is connecting communities if those communities aren't represented proportionately in its staffing."
Luckie's note provides an inside look at what it's like to be black inside of Facebook, but it is not the first time Facebook's lack of diversity has been exposed.
"You can build something that works, that people want to use, but you can't actually make all the right decisions if among the builders there's not enough diversity and perspective," Facebook's head of diversity Maxine Williams told CNBC in July.