Thousands of unionized workers of GM Korea Co., the South Korean unit of U.S. automaker General Motors Co., voted in favor of a strike, an official said Thursday, a move that may set the stage for a walkout.

The official said 71 percent of more than 13,600 unionized workers voted for the strike, though they could not immediately stop working.

By law, a union cannot go on strike during mediation by the state-run National Labor Relations Commission which usually lasts 10 days.

The company official said the vote results do not necessarily mean that the union will immediately go on a strike.

"GM Korea is making utmost efforts to reach a fair and reasonable deal based on mutual trust and understanding with the union," the company official spoke on the condition of anonymity, citing the issue's sensitivity.

Repeated calls to the union seeking comment went unanswered.GM Korea's unionized workers staged a partial strike in 2013, but they did not strike in 2014 or 2015. (Yonhap)