I don't think any company of any size could just say no. No corporation has enough power to stand up to the government if the government is determined. They do

I don't think any company of any size could just say no. No corporation has enough power to stand up to the government if the government is determined. They do have a lot of soft power to keep things from getting to that point. They can spend a lot of money to influence politicians and the public and apply pressure to the government to back down. Walmart, for example, has ~2.2 million employees. Even if Walmart did something egregious enough to have their charter revoked would you want to be the governor of the state that has to tell those 2.2 million people they don't have jobs tomorrow? Not to mention the enormous ripple effects that would have through the economy. I've seen a lot of people argue that what the banks did during the lead up to the financial crisis was egregious enough to warrant the corporate death penalty, but those institutions were so critical to the economy that they couldn't be shut down. So, in a sense, there are already quite a few companies that are too large for the government to effectively exercise it's power over. I don't think there is a set number though. It probably depends a lot more on what the business does and how central it is to the health of the economy. It's the "too big to fail" debate, and at various times in the recent past, we have determined several automakers and financial institutions to fall into that category. I think if you are too big for the government to let you fail, you are too big for the government to try to shut you down.