It was one of the big selling points of this massive development project in the heart of Harlem: a new Civil Rights Museum led by the Rev. Al Sharpton.

But in a letter to developers on Monday, Sharpton, who leads the foundation behind the museum, said the space was inadequate and asked for it to be dedicated to affordable and senior housing instead.

“We do not see how this can be done in the confines of the available space,” Sharpton said in the letter. “We strongly urge you to use the space that we are releasing to provide more affordable housing and senior housing, which has been the express desires of many in the Harlem community.”

The One45 project in Harlem needs the City Council rezoning approval to build two residential towers with 900 apartments, about 250 of them affordable.

It was approved by the City Planning Commission last week, but faces strong local opposition, including from the community board.

The project includes the new headquarters for Sharpton’s National Action Network and a geothermal system for clean energy heating and cooling.

Next week, it will come before the City Council’s Land Use Committee.

“It is building housing in a community that is low income and that has had a lot of displacement over the past ten, twenty years,” Councilwoman Pierina Sánchez said. “The project itself does not propose affordable housing that is affordable for the community.”

Harlem councilwoman Kristin Richardson Jordan strongly opposes the project, demanding developer Bruce Teitelbaum dedicate most of the units to be affordable for low-income residents.

“Teitelbaum is disingenuous and has no real desire to work with the community to make One45 a great development,” Richardson Jordan said in a statement. “I will only support housing in Harlem that reflects what Harlemites can afford.”

“I urge the City Council to stand against gentrification, and to handle the housing crisis we are currently facing by supporting fully affordable options,” she added.

Many of Richardson Jordan’s colleagues in the Council agree and are willing to defer to her once the project comes for a vote.

“The face of Harlem has changed significantly throughout the years and we want to make sure that we are protecting, you know, the historical roots of the community, and I think that really imposes on us a mandate to be responsible when we are approving these projects,” said Manhattan/Bronx Councilwoman Diana Ayala, who’s also the Council’s deputy speaker.

Teitelbaum says the project is still on. A much smaller, all-market-rate building wouldn’t require Council approval. He could also build a storage facility instead.  

And on the museum front, the Civil Rights Foundation said it’s considering two other locations here in New York City.