When can employees strike?

do u have to be part of a union first? are there other rules? i work for a huge private corporation in which i and one other person run an entire operation grossing over 250k per year. we both make less than 24k, and fine with that but we've had an equipment order in for a year now (for a 2k computer to replace the one we've got that's slowing us down from 7 years ago) and we've had an order to add one staff in for almost six months. we are swamped and increasingly it is only me because the other is about to go on her pregnancy leave and is having complications. in the meantime, for a position that requires six months of training, i have less than three months left now to train one, while operating and managing what is necessarily a three-person operation, solo. and they purposely delayed authorization of the 3rd person (who is now increasingly going to have to be the 2nd person) since january. believe me i have tried reasoning. even from a business perspective they are blind.