If you dislike fossil fuel companies, build one that obsoletes their business model (e.g. Tesla). If you dislike mining operations for employee mistreatment, start a company based on fair trade products (e.g. Fairphone). And if you care about these causes, support them with your wallet and evangelize them.

People say these companies are too big to compete with, but they used to say the same thing when these companies are created. Feel free to strike, but remember you can also vote to your feet, your wallet, and your labor.