A Philadelphia City Council member has proposed a bill that would require the city’s nonprofit groups to annually certify under penalty of perjury that they are “purely public charities” and thus eligible for municipal tax breaks, according to NewsWorks, an online affiliate of public radio station WHYY.

Councilman Bill Green, who introduce the measure last week, said the legislation aims to curb tax exemptions on charity-owned properties used for commercial purposes, and to encourage nonprofit organizations to voluntarily contribute more to city coffers to cover the cost of municipal services.

Such payments in lieu of taxes have declined in Philadelphia from more than $9-million in 1995—when then-Mayor Ed Rendell pledged not to challenge charities’ tax-exempt status in exchange for higher contributions—to $383,700 in 2011.