A group of former employees and board members of the Smithsonian’s National Museum of African Art have written a letter charging the museum with promoting a culture of racism and saying formal reports about racial bias and attacks have been ignored.

In a letter sent last week to Smithsonian Secretary Lonnie G. Bunch III, the unidentified individuals say that more than 10 former and current black employees of the museum dedicated to African art and culture have experienced “incidents of racial bias, hostile verbal attacks, retaliation, terminations, microaggressions and degrading comments” that date back at least five years.

The museum’s staff is predominantly white, with no curators of color, and complaints by black employees about their treatment have been systematically disregarded, according to the letter, first reported by HuffPost.

Bunch did not respond to a request for comment, but the Smithsonian released a statement Wednesday in response to the letter emphasizing the museum’s commitment to diversity. The museum leaders “are cognizant of the need to recruit, employ and empower more curators and artists that represent diverse fields and backgrounds,” the statement said. “While our collections and exhibits represent a rich diversity of thought, artists and scholarship, we recognize that we must continue to increase diversity within the museum, and drive inclusive behavior among all Smithsonian staff.”

One of the smallest branches of the Smithsonian, the National Museum of African Art has a staff of 29, with six black employees and one Latino, according to Smithsonian spokeswoman Linda St. Thomas. None of its three curators are black, St. Thomas confirmed.

Three directors have led the museum since 2008 and all of them are black. Johnnetta Cole, a nationally recognized advocate for museum diversity, was the director from 2008 to 2016. She was succeeded by Gus Casely-Hayford, whose two-year tenure ended earlier this year. Deborah L. Mack was recently appointed interim director.

Cole had no comment when reached Wednesday. Casely-Hayford could not be reached in London, where he is now director of the V&A East, a satellite of the Victoria & Albert Museum. Mack became interim director in March, after the museum closed because of the coronavirus pandemic. A veteran of the Smithsonian’s National Museum of African American History and Culture, Mack said that the complaints are the result of an overburdened staff, not racism.

“A number of these issues are conflated with chronic understaffing,” Mack said, noting that the museum had 60 employees in 2000, compared with its current 29. “The museum is very inward-looking. It hasn’t been able to stay up to speed with 21st-century museum practices.”

Several employees are doing the work of two and three positions, Mack said, adding that she is hiring for 14 open positions, which should help to increase staff diversity.

“I do not like the fact that, at present, there are no black or African curators. And just being black isn’t enough. In this field, we are a complex and multinational people. It’s our obligation to have that representation on staff,” she said.

Milton Jackson, a former African Art museum educator, told the New York Times that he is one of five individuals who signed the letter. Jackson filed a formal discrimination complaint against the museum in 2016.

The letter makes seven recommendations, including the removal of deputy director and chief curator Christine Mullen Kreamer, a veteran employee the writers describe as favoring white staff and bullying and harassing their black colleagues. Kreamer responded to a request for comment by directing a reporter to the Smithsonian press office.

The writers also ask that Kreamer’s position be separated into two and that the museum review all firings and racial complaints. They seek the development of a pay-equity plan for black employees and a public commitment to improving staff diversity and career advancement for black employees.