In a statement Wednesday, said she would not cross a picket line to participate in the debate, scheduled Dec. 10 in Los Angeles. Most of the other candidates quickly followed.
CBS is to broadcast the debate, which is co-sponsored by the Democratic National Committee.
"It is my hope that both sides will reach an agreement that results in a secure contract for the workers at CBS News, but let me be clear: I will honor the picket line if the workers at CBS News decide to strike," Clinton said.
, on a conference call with reporters, said he would not cross the picket line in the event of a strike. Spokesmen for , , and also said those candidates would not participate.
CBS News writers on Monday authorized their union leaders to call a national strike. About 500 of the network's television and radio news writers in New York, Los Angeles and other cities have been working under an expired contract since April 2005.
CBS News called the vote "unfortunate" and said its latest offer was "fair and reasonable."
Democratic spokeswoman Karen Finney said the committee would monitor the CBS labor situation, and she indicated the party would cancel the debate in the event of a strike.
"The Democratic Party believes the right to organize and collectively bargain is one of our most fundamental rights, and we are proud to stand with the working men and women in the labor movement," Finney said. "Given the Democratic Party's long history of supporting the labor movement in America, if the strike is still going on, we will not cross the picket lines."
The DNC recently announced it would move its winter meeting from Baltimore to suburban Virginia west of Washington because of a labor dispute at the Baltimore hotel.