McDonald's black franchisees are choosing to leave the chain as the disparity in performance between their restaurants and their white counterparts grows, Business Insider reported Monday.

The average cash flow of black franchises is much less than the average cash flow of all of the chain's restaurants, the report said, citing franchisees, former corporate employees and internal documents viewed by Business Insider.

The gap has grown over time. In 2012, it was less than $24,600 per month and in 2017, it was about $60,600, according to documents from the National Black McDonald's Owners Association, or NBMOA, cited by Business Insider.

Some African American franchise owners are leaving the system. In 2008, there were about 304 black franchisees at the chain, but by 2017, there were 222, according to documents from NBMOA.

"It is among our top priorities that all McDonald's franchises in all communities have the opportunity to prosper, grow and achieve their business ambitions," McDonald's said in a written statement to CNBC. "These efforts are rooted in our core belief that diversity and a vibrant, inclusive and respectful McDonald's makes us stronger. McDonald's is proud to foster opportunities for entrepreneurship, economic growth and mobility in communities across the country."

Business Insider's report said that black franchises are much more likely to be located in places where sales are lower and costs like security are higher.