The Philadelphia Historical Commission, tasked with ensuring that the city's historically significant spaces are preserved, could see its budget nearly double under legislation introduced in City Council on Thursday.

The bill would let the commission charge fees when staff review an application to build on or alter a designated historic site. The city has estimated that the measure would raise about $350,000 annually, a sizable influx for an office that operates on a $424,560 annual budget.

"I believe that this fee will help to bolster the Historic Commission staff, enable the commission to better review applications for historic dedication, and help preserve the historic fabric of our city," Councilman Mark Squilla, one of the bill's sponsors, said in a statement.

The commission, consisting of five staff members, has been operating on essentially a flat budget for years, even as the number of historic districts and permit applications has increased. The staff weighs all building and construction projects on historically designated properties. But other critical functions the agency is mandated to perform have largely fallen by the wayside.

Critics complain that the commission is supposed to seek out historic sites and districts and designate them, but it performs that task only sporadically. They also say the commission has not inventoried the city's historic resources and is slow to designate nominated properties, activities that require staff and resources in short supply.

Mayor Kenney has long advocated increasing the commission's funding. In 2014, while he was a member of Council, he introduced a bill that would have allocated $500,000 to the commission and another that would have added at least 1,000 properties to the city's register of historic places.

He resigned to run for mayor before the legislation was passed.

His administration supports the legislation introduced Thursday, which was cosponsored by Squilla, Councilwoman Blondell Reynolds Brown, and Councilman Al Taubenberger.

Anne Fadullon, director of the Office of Planning and Development, and Jon Farnham, director of the Historical Commission, said in a joint statement that reviewing permit applications strains the commission's small staff.

"Assessing these fees is anticipated to allow the Historical Commission to expand its staff and, ultimately, allow the commission the strengthened capacity to proactively designate properties as historic," they said.

The new fee would be calculated at 25 percent of the cost of the associated building or demolition permit. Permit costs vary depending on the size and type of project.