More than 12,000 U.S. film and television writers are on strike, stalling production of entertainment shows and threatening film production in Hollywood. Mike O'Sullivan reports from Los Angeles, the writers walked out after negotiators failed to reach agreement on key issues.

The first picket lines went up early Monday at New York's Rockefeller Center, home of the National Broadcasting Company. Within hours, picketers appeared outside the production centers of networks and studios at more than a dozen Los Angeles locations, from Disney to Paramount.

"What do we want? A fair contract. When to we want it? Now."

Screenwriters walked out of talks Sunday after failing to reach agreement with producers over residual revenues for Internet downloads of television shows and movies. The download market is small but is expected to grow. DVD residuals and other issues were also up for discussion. This Los Angeles striker says screenwriters want their share of revenue from producers.

"If they make money off of our product, we get some of that money," he said.

The most immediate impact will be on late night television shows that use topical skits and jokes related to news events. Several have announced they will stop new production and re-run old shows. Other network series have stockpiled scripts for future use. Movies would only be affected by a long strike because the screenplays for current productions have already been written.

Los Angeles Mayor Antonio Villaraigosa says a long work stoppage would hurt his city.

"This is the entertainment capital of the world," said Antonio Villaraigosa. "There are some 225,000 jobs associated with the entertainment industry, 455,000 jobs associated with the creative economy. So make no mistake, this is going to have an impact on the economy of Los Angeles."

A 22-week writers' strike in 1988 cost the entertainment industry an estimated $500 million. Los Angeles economist Jack Kyser says a similar strike today would cost $1 billion.

Film and television production create an estimated $30 billion in economic activity in Los Angeles each year. The effects of the strike will ripple through the economy, affecting not only writers but also actors, directors, and camera operators, and the electricians, drivers and others who work in the industry.