Unions are being hurt by the fear that their targeted company will plunge into bankruptcy if they go on strike. In the case of Northwest Airlines, other unions did not join the mechanics on strike in part because of a lack of labor solidarity, but also because they may have feared that a widespread strike would bankrupt the airline, ultimately causing the workers to lose their jobs.
See "Airlines' Woes May Erode Unions' Clout", James F. Peltz, Los Angeles Times, August 25, 2005