The New York Times reports on a movement underway among Walmart employees to back a group working toward better pay and benefits and respect at work. It is not a union (though the effort has had union financial help) and does not aim to organize local unions or enter collective bargaining.
Walmart, naturally, isn't happy about any collective actions by employees, grassroots or not. They see it as a stalking horse for union organization and a way to drive up Walmart wages as a way to help unionized workers at other chain stores.
Read about OUR Walmart at its website.
For now, federal labor law protects workers who engage in collective discussion and action. What do you bet the Walmart lawyers have some ideas on how to remove protection for such free speech?