City officials suspect that 40 percent of Los Angeles' 11,000 billboards were installed illegally, and that the city Building and Safety department has not been enforcing the billboard laws.

In 2002 the LA City Council voted to require city inspectors to inventory all existing billboards. One month later the billboard companies filed a federal court injunction which stopped the inventory effort.

A 2006 legal settlement with the city allowed the billboard companies to begin converting a portion of their billboards to electronic LED displays. In return the companies agreed to provide the city with a list of all their billboards, both legal and illegal.

Two weeks ago the City Council learned that rather than providing the list, the companies instead delivered several boxes of documents and an unreadable electronic file purporting to contain the list.

CBS and Clear Channel, two of the largest billboard companies, are now suing the city to prevent it from releasing any list of billboards to the public, on the grounds that such a list constitutes a "trade secret."

City activists have demanded that the list be made public so they can protest the billboards that illegally deface the city.

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