On Tuesday, the manager, vocal diversity advocate Mark S. Luckie, made public a memo he sent to Facebook's global staff before leaving the company on November 16.

In the memo, Luckie said black people make up some of the most active users on Facebook but the company itself is not nearly as diverse. Black employees now make up 4% of the company's US workforce in 2018, up from 2% in 2016.

"The population of Facebook employees doesn't reflect its most engaged user base," wrote Luckie, who worked as a partnerships manager at Facebook focused on managing relationships with global influencers from diverse backgrounds. "There is often more diversity in Keynote presentations than the teams who present them. 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, who worked at the company for a year, said that Facebook's lack of black representation among employees has an adverse impact both on users and its black staffers.

"Black people are finding that their attempts to create 'safe spaces' on Facebook for conversation among themselves are being derailed by the platform itself. Non-black people are reporting what are meant to be positive efforts as hate speech, despite them often not violating Facebook's terms of service," Luckie wrote, linking out to past media coverage of the issue.

Moreover, Luckie said black employees are frequently asked to provide input on projects involving race rather than the company hiring people from diverse communities on teams -- a more "effective" approach, he wrote.

"At a company whose family of products directly affects the lives of 2.5 billion people worldwide, representation and inclusion should be of the greatest importance to everyone," wrote Luckie, who ended the memo with 10 recommendations for improving diversity and inclusion at the company.

Among the recommendations is creating an internal system for employees to anonymously report microaggressions and establishing more focus groups with users from underrepresented communities to understand their experiences on Facebook and Instagram.

In a statement sent to CNN from Facebook spokesperson Anthony Harrison, the company said it has been "diligently" working on increasing diversity over the last few years.

"The growth in representation of people from more diverse groups, working in many different functions across the company, is a key driver of our ability to succeed," Harrison said. "We want to fully support all employees when there are issues reported and when there may be micro-behaviors that add up. We are going to keep doing all we can to be a truly inclusive company."

Luckie has been open about his experience at previous jobs, too. Prior to joining Facebook, Luckie worked at other tech firms, Reddit and Twitter. After leaving Twitter in May 2015, he wrote a Medium post about what it was like to work at a tech firm as a black man.

"The widespread underrepresentation of faces of color in tech is already alarming," wrote Luckie, who was previously an editor at the The Washington Post. "However, the situation is more dire than raw numbers project."

On a call with CNN on Tuesday, Luckie said he's making the Facebook memo public because "Facebook does not make any meaningful change on a company level unless it is being held accountable publicly."

Luckie said when he published the original memo on the company's internal Facebook platform, "there was no response from executive leadership. That is uncharacteristic for something that generates this much conversation. I know they were talking about it."

Luckie said the move to send the memo to Facebook's global staff felt like "going out on a limb by myself." But he said "at least three people came up to me and said they handed in their resignation for the same reason," he told CNN.

"One of them even put it in that day," Luckie said.