A pay cut would be an "over my dead body" issue for many unions.
Edit: Since this apparently does not go without saying, the feedback loops in a union are all wrong for taking that kind of risk (remember, the pay cut does not guarantee company survival). People willing to rock the boat with calculated gambles like that do not rise to positions of authority in a union.
That depends on where you are.
If I recall correctly, In ~2009-2010 German automotive unions worked together with management and employees and negotiated widespread reduction of work hours in order to prevent layoffs.
Of course unions/employee representatives have a different place here(e.g. half of members of the board of directors are elected representatives of employees.)
Edit: Since this apparently does not go without saying, the feedback loops in a union are all wrong for taking that kind of risk (remember, the pay cut does not guarantee company survival). People willing to rock the boat with calculated gambles like that do not rise to positions of authority in a union.