No. Employees have a legal right in this country to organize, form unions, and strike. It is illegal to retaliate against an employee who engages in these activities.
Nonetheless, some employers still retaliate. According to Reuters, Walmart was recently the subject of action by the National Labor Relations Board for retaliation.
“Groups of Walmart workers went on strike nationwide on Nov. 22, 2012, to protest the retailer’s wages and worker benefits. The day after Thanksgiving, known as Black Friday, is typically the busiest shopping day of the year. The workers also went on strike in May and June before the company’s annual shareholder meeting.
The company retaliated against employees who joined those strikes by firing them, threatening to fire them or disciplining them, the NLRB said in a statement on Monday. The labor board also said that a Walmart spokesman made comments on television threatening workers who planned to join the November protests.” http://www.reuters.com/article