I wonder what reasonable rights we can have to protect workers. At will employment sounds like a good idea on paper (employee can quit anytime they want), but

I wonder what reasonable rights we can have to protect workers. At will employment sounds like a good idea on paper (employee can quit anytime they want), but it is assymetric, especially when large corporations are involved (employee is easily replaceable and so impact of quitting is less on corporation). Perhaps we should have at will employment for small corporations and then private unions for larger corporations? The unions will increase bargaining power of employees which could mitigate the issues brought up in the article.