A US independent federal agency has accused Honda Motor of violating laws that protect workers' rights, saying it unlawfully suppressed an effort to organize a labor union at its plant in the state of Indiana.

The National Labor Relations Board filed a complaint against the Japanese automaker on Tuesday.

The accusations include instructing workers to remove stickers of the United Auto Workers union from their helmets and threatening disciplinary action against union supporters.

A hearing before the board's judge is scheduled for October.

Honda says the allegations of wrongdoing in the complaint are without merit and the company will cooperate in the hearing.

The automaker says filing unfair labor practice charges is a common tactic used by the labor union to generate publicity and attention for their organizing campaigns.

The UAW won big pay raises from the management of three major carmakers last year. It has been encouraging workers at plants of foreign auto firms in the US to unionize.