The Democratic National Committee made the official announcement tonight.
"Due to the uncertainty created by the ongoing labor dispute between CBS and the Writers Guild of America, the DNC has canceled the December 10th debate in Los Angeles. There are no plans to re-schedule," said DNC communications director Karen Finney.
Most if not all of the Democratic candidates had already said they planned to boycott the debate if the long-running labor dispute wasn't resolved, so the announcement was little surprise. But the formal announcement was still a setback to CBS News. The debate had been scheduled to be moderated by CBS News anchor Katie Couric.
CBS News in a statement said it regrets not being able to offer the Democratic debate.
"The possibility of picket lines set up by the Writers Guild of America and the unwillingness of many candidates to cross them made it necessary to allow the candidates to make other plans," CBS News said in a statement.