This union is based upon the labor union model. Check out what Monica Johnson had to say about the idea behind it.
Mass default would be much like a strike, and used as a last resort. This is being discussed widely, and I'm pleased to hear that. As Johnson says in the interview, "it's a strategy of refusal."
This is precisely why a debt jubilee is necessary. The system has been rigged against us, and it's time to act collectively. A strike sounds reasonable to me. What do you think? Do you think a debtors insurrection makes sense?