Ryan Gravel, the man behind Atlanta’s increasingly popular Beltline, resigned Monday from the organization that helps raise funds for the project, according to a news report.

Gravel and Nathaniel Smith, founder of the Partnership for Southern Equity, turned in letters of resignation to the Atlanta BeltLine Partnership citing concerns over affordability and equity along the growing trail and pedestrian greenspace, according to Maria Saporta of Saporta Report.

Affordability along the Beltline has become an issue as its popularity has pushed housing prices up and raised concerns that could displace current residents.

Atlanta Beltline, which oversees the development of what will be a 22-mile loop through the city, has said it hopes to raise $7.5 million to encourage affordable housing development.

However, Gravel and Smith said in their resignation letter that that funding is far from what is needed.

“The recent announcement of $7.5 million from TAD bonds, for example, will likely support fewer than 200 affordable units out of ABI’s obligation to 5,600 – it is a drop in the bucket when compared to the need,” the pair said in their letter.

“As the economy roars back to life and growth in the city accelerates, this work is increasingly urgent and we feel strongly that our attention must be channeled directly toward it,” they said.