The availability of affordable, multifamily housing for an urban workforce has long fueled the socio-economic vitality of America’s leading cities. It has provided hardworking young people, immigrants and minorities a sturdy ladder toward the American Dream.

But some of the rungs on that ladder are missing today. High-end apartment and condominium complexes dominate housing development inside the top tier urban markets. Median rents are setting new records at levels that are well out of reach for the workforce, even for those who make 100 percent of their local median income.

For our largest cities to be truly great cities, a housing pathway that accommodates a middle class workforce is essential.

Historically, our great cities have served as models of upward mobility, reinforcing opportunities to advance through hard work and self-sufficiency in pursuit of a better life. But how does a capitalistic democracy survive when the majority of a city’s workforce is economically excluded from experiencing the great teaching hospitals, colleges, art, culture and commerce of a given state?

America’s top mayors understand what is at stake. To prevent economic segregation among their constituents, New York City Mayor Bill DeBlasio, Boston Mayor Marty Walsh, San Francisco Mayor Ed Lee, Washington, D.C., Mayor Muriel Bowser and others are pursuing a wide range of housing strategies.

In Boston, for example, Mayor Walsh has begun to make progress toward an ambitious goal of 53,000 new housing units by 2030. He has beefed up the city’s inclusionary zoning to increase developer contributions toward affordable housing and to encourage more housing outside the downtown.

This kind of leadership demands our active support, but more dramatic steps are needed to facilitate workforce housing options here and in our top tier cities. The most meaningful solution will require the public and private sectors joining forces to develop housing at appropriate rent levels.