WASHINGTON (Reuters) - The U.S. National Labor Relations Board (NLRB) on Wednesday issued a complaint against Wal-Mart Inc, alleging the world’s largest retailer violated labor laws in 14 states by taking action against striking workers.

A man chants outside Wal-Mart during a protest for better wages and working conditions during Black Friday in San Leandro, California November 29, 2013. REUTERS/Stephen Lam

A complaint issued by the NLRB’s general counsel’s office said Wal-Mart 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.

More than 60 Wal-Mart supervisors and one corporate officer are named in the filing.

“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,” said Brooke Buchanan, a spokeswoman for the world’s largest retailer.

The NLRB, the federal agency that oversees union elections and polices unfair labor practices, investigates 20,000 to 30,000 allegations of National Labor Relations Act violations made annually by employees, unions and employers. More than half are withdrawn or dismissed.

In the Wal-Mart case, a preliminary investigation by the NLRB revealed that charges against the retailer likely had merit. Settlement negotiations were unsuccessful, so one of the board’s 26 regional directors issued a complaint detailing the alleged violations.

Most of the allegations in the complaint released Wednesday focused on management’s response to Wal-Mart workers who participated in strikes at stores in California, Kentucky, Texas, Washington and elsewhere in May and June 2013.

Dozens of employees received verbal and written warnings, formal reprimands and were otherwise disciplined after striking last year for improved wages and working conditions at Wal-Mart stores, according to the complaint.

Wal-Mart also since May 2013 has improperly categorized workers’ time spent participating in legally protected strikes as unexcused absences, the complaint stated.

The NLRB seldom puts out press releases about complaints it is issuing, but it did on Wal-Mart.

The retailer has known since November 2013 that the agency had authorized issuance of a complaint, but a settlement has not been reached. Wal-Mart now has until January 28 to respond to Wednesday’s filing.

The next step is for an NLRB administrative law judge to oversee a trial to determine whether Wal-Mart broke the law. The judge’s findings will then be adopted or rejected by the five-member board.