Which of the following were methods used by labor unions to secure better working conditions?

collective bargaining
piecework
strikes

strikes

Explanation:

The labor movement in the United States grew out of the need to protect the common interest of workers.  

To get their demands, the unions rely on various strategies, like strikes:

Workers refuse to return to work until their demands are fulfilled. The company comes to a standstill and consent to granting the union's demands.

what are the options?

bye cutting off more workers so the graph can go back up