AMONG the many issues Philadelphia's new mayor and City Council members will be faced with when they take office next year is expanding and preserving affordability in neighborhoods undergoing gentrification, which must be at the forefront. We have an opportunity to be a leader in a growing national conversation about addressing this issue if the public officials we elect enact bold policies that set it apart as a priority.

The Philadelphia Coalition for Affordable Communities (PCAC) - a growing coalition currently made up of more than 30 of the city's leading community, disability, faith, labor and urban-agriculture organizations - recently released a proposal that can help us become such a leader. United under a campaign called Development without Displacement, we recently released an anti-speculation tax proposal that would generate up to $12 million a year for the Philadelphia Housing Trust Fund, doubling the current resources in the fund without raising taxes or creating new fees for a large majority of residents.

Our proposal calls for increasing the realty-transfer tax by 1.5 percentage points on properties in the City of Philadelphia that are resold less than two years after being purchased, otherwise known as "flipped houses." In 2013, more than 6,000 real-estate transactions in the city fit this description, an estimated total value of $782 million. Those numbers make clear that developers are reaping huge profits, which is fine so long as it is done while respecting the communities in which they are operating.

Too often, we forget that Philadelphia remains among the nation's poorest major cities - home to a large population of children, disabled individuals, seniors, and working families living below the poverty line. Many of the neighborhoods in which these people live have become targets of house-flipping developers, as numbers show that a majority of these transactions have been concentrated in gentrifying neighborhoods.

When a developer successfully flips a house, it immediately raises the value of the surrounding real estate, which on the surface can seem like a good thing. But citywide, and in our neighborhoods, change in household income has not kept pace with changing housing costs. Between 2000 and 2012, the city's median household income decreased by 13 percent, while median gross rent increased by 15 percent and the median home-sale price increased by 51 percent.

More than 240,000 households citywide are forced to spend 30 percent or more of their income on a place to live. These households are "housing cost-burdened," which means that the proportion of income spent on housing limits their ability to afford other basic needs. More and more of our neighbors, particularly those who rent, find themselves in this situation - struggling to make ends meet.

There is a tool available to help those in need afford their changing neighborhoods: the Philadelphia Housing Trust Fund. Now entering its 10th year, the fund provides dollars to support the development of new affordable homes, helps existing homeowners make critical repairs and prevents foreclosures and homelessness. It has provided housing opportunities to more than 14,000 low- and moderate-income families, seniors, disabled and homeless people to date.

Our research found that an additional $12 million investment in the fund has the power to create 240 units of newly-constructed, affordable rental apartments; support 150 existing homeowners seeking critical home repairs and 112 home modifications to assist those with disabilities; stabilize 272 households facing homelessness; and provide 240 grants for capital improvements and infrastructure for community gardens and food-producing green spaces. That is a major impact on many lives throughout our city in desperate need of the assistance.

So, when you read up on candidates or possibly meet them at events, check to see that their public-policy goals encourage equitable community development and represent plans that include people of all income levels in the future of our neighborhoods. With the right mix of affordable housing, job creation and urban-agriculture policies, we can help create diverse, healthy neighborhoods.

An anti-speculation tax applied to a few in order to benefit many is a real opportunity to chart a course toward that outcome.