Nearly 500 activists and union members marched alongside elected officials in a march by the “Real Affordability for All” coalition this afternoon in Harlem.

The event marked the largest public demonstration to date by the group of 50 housing advocacy and anti-poverty groups that’s calling for at least 50 percent affordable housing in all new developments, as participants took part in a 10-block march north from 116th Street to 125th Street along a closed-off Adam Clayton Powell Jr. Boulevard after a series of speeches at the First Corinthian Baptist Church.

“We’re here today because there’s a crisis in this city,” Rev. Michael Walrond Jr., the church’s senior pastor and a former candidate for Congress, told the audience. “There are people in this city who are struggling to find housing and many of them are here in this audience.”

Elected officials like Public Advocate Letitia James and several City Council Members led rousing chants at the church and the marchers joined in with increased numbers through a new alliance with the Building and Construction Trades Council of Greater New York, a group of 15 local construction unions that support the coalition’s affordable housing requirement proposal.

“We are here because we believe in the same thing,” said Gary LaBarbera, president of the council. “And that is justice.”

Political observers are watching the coalition’s progress closely to gauge its members’ success in pushing for a substantially higher number of affordable units in new developments while burnishing their close alliances with Mayor Bill de Blasio.

“Whoever gets voted in, we’re going to put pressure on them so they do what they said they were going to do,” said Loraine Knox of Community Voices Heard as she walked in the march. “Hopefully, since he’s new he’ll do the right thing.”

The mayor’s office didn’t respond to a request for comment.