Walmart has been the subject of an ongoing campaign by those opposed to its treatment of employees. Lucy Nicholson/Reuters

The National Labor Relations Board (NLRB) issued a complaint against Walmart on Wednesday, alleging the world's largest retailer violated labor laws in 14 states through actions it took against striking workers.

A complaint issued by the NLRB's general counsel's office said Walmart representatives appeared on national news broadcasts and threatened to retaliate against workers if they went on strike. It also alleged they disciplined and fired workers for engaging in legally protected protest activity.

According to the NLRB complaint, 19 employees were discharged “allegedly as a result of their participation in activities protected by the National Labor Relations Act.”

More than 60 Walmart supervisors and one corporate officer are named in the filing.

Brooke Buchanan, a spokeswoman for Walmart, said, "We believe that our actions were valid. We take our obligations very seriously. We look forward to sharing our side of the facts in these cases with a judge."