What does Cardcheck mean in Union Lingo?

If you want to form a Union 50% of the employees have to sign a card that they want one. The employer can grant it or call for a vote. In this time they will try to threaten, coheres and fire employees usually. Don't take it, being Union is the only way I can put food on the table for my family and make a decent wage to live. Union till i die! Union girl