The US National Labor Relations Board issued a formal complaint Wednesday against giant retailer Walmart, saying it violated labor rules by threatening and punishing workers who joined pro-union protests. The complaint says that the country's largest employer and a longtime foe of unions violated employee rights in 14 states during the November 2012 Thanksgiving holiday protests. The NLRB complaint, which consolidates a number of separate cases, involves more than 60 employees, including 19 who were fired or laid off illegally after taking part in the protests. It names 60 Walmart supervisors and one corporate officer for taking action against workers that allegedly violated their rights. At stores in numerous states, Walmart "unlawfully threatened, disciplined and/or terminated employees" for legally joining the protests and engaging in other legal activities that November, the NLRB said in a statement. "The National Labor Relations Act guarantees the right of private-sector employees to act together to try to improve their wages and working conditions with or without a union." The NLRB issued the complaint after giving the company time to reach settlements with complainants that did not resolve the problems. The complaint deal with a nationwide campaign by pro-union Walmart workers and supporters from union groups during the 2012 Thanksgiving weekend, normally the heaviest shopping period of the year. The protesters highlighted the company's low wages and tough working conditions, garnering widespread media attention. In November, the NLRB accepted most of the workers' complaints, finding Walmart in violation of the law for its actions against workers, but gave the company time to try to settle them. The complaint gives Walmart until January 28 to respond, after which a hearing will be held under an administrative law judge, according to NLRB procedures. Walmart said it would show in the hearing that it acted legally. "This will allow Walmart to shed some light on the facts and present our side of the case," company spokeswoman Brooke Buchanan told AFP. "We continue to believe we acted lawfully, and treated the associates with respect. "We did not terminate any associates based on their association with an organization." Instead, she said, they were dismissed for not fulfilling the normal requirements of their jobs. In a statement, the pro-labor group OUR Walmart, supported by the United Food & Commercial Workers International Union, said Walmart has a history of firing workers who have advocated for more rights and unionization. "Since the start of the year, Walmart has continued to retaliate against workers who speak out for better jobs," they said. The NLRB action "will provide additional protection for Walmart's 1.3 million employees when they are calling for Walmart to publicly commit to paying workers a minimum of $25.000 a year for full-time work."