By John McDevitt

PHILADELPHIA (CBS) – A billboard near the Benjamin Franklin Bridge is preventing construction of a high-rise apartment building at 2nd and Race streets in Old City.

Many are wondering why the billboard company is holding the cards.

The owner of the billboard, Keystone Outdoor Advertising Company, threatened to take legal action against the high-rises developer Brown/Hill –concerned that building could block the billboard.

The developer revised building plans making it less broad but adding two floors. The design went from 197 feet to 222 feet.

But current zoning doesn’t allow a building to be that high. Enter 1st District Councilman Mark Squilla, who has introduced a bill to change the restrictions around the bridge.

Stephanie Kindt is with General Council for Scenic Philadelphia, a public space advocacy group. She says the legality of the billboard itself, is not being challenged.

“The city’s zoning code clearly does not allow billboards along any of our bridges,” said Kindt. “The federal highways’ does not allow three face signs along federal lane highways.”

She says this is one of many signs in Philadelphia that are there by exception.