More than 12,000 television and film screenwriters exchanged pens for picket signs yesterday… More than 12,000 television and film screenwriters exchanged pens for picket signs yesterday after last-minute negotiations between the writers’ unions and producers proved unsuccessful.

The contract dispute was over the writers’ demands for a large increase in pay for movies and television shows released on DVD and for a bigger share of the revenue from work delivered over the Internet, according to The New York Times.

The strike, which is the first walkout by writers since 1988, could affect everything from soap operas and daytime talk shows to primetime programming and late night comedy shows, depending on how long it continues.

Some of the effects of the strike could be seen as early as yesterday – when daily shows like “The Late show with David Letterman” and “The Tonight Show with Jay Leno” were forced to air reruns –