Four City Council members joined late Wednesday in a legal challenge to the permit for a proposed Downtown electronic billboard.

Council President Doug Shields and members William Peduto, Bruce Kraus and Ricky Burgess filed appeals of zoning administrator Susan Tymoczko's approval of a 1,200-square-foot sign for the front of the new Grant Street Transportation Center. They joined Councilman Patrick Dowd, who filed an appeal Tuesday that will trigger an April 10 zoning board of adjustment hearing on the matter.

Councilman Jim Motznik yesterday blasted a proposed moratorium on new billboard permits that Mr. Kraus plans to introduce Tuesday.

"You cannot tell a business that they cannot operate inside the city of Pittsburgh," Mr. Motznik said.

Mr. Kraus said he is concerned about uncontrolled expansion of signs.

Last month an unidentified caller asked city zoning officials about the process for expansion of the landmark Bayer sign on Mount Washington, according to e-mails from Ms. Tymoczko to council. Mr. Kraus said he was concerned that a dramatic change in the sign, owned by Lamar Advertising, could "corrupt" something that is "perceived to be an historic landmark in this city."