How Did the Unions ever get a Collective Bargaining Agreement? Will CBA's be Abolished?

How did unions such as the NTEU ever get any sort of agreements or contracts with government agencies, if they don't have any leverage (we can't strike)?

Was it just the good will of the people at the time? Growing up in a world where businesses embrace greed and dont give anything out for free, how did the NTEU and other unions get us all of the protections that we enjoy today?

Do you think once these contracts expire, the government will just do away with any sort of agreements? I'm genuinely curious how they ever had any teeth to begin with in order to negotiate.

Share your thoughts and shout-out to all the others "holding the line"