A union representing engineers and technical workers at Boeing Co filed a complaint with the National Labor Relations Board accusing the airplane maker's security personnel of stopping union members from distributing leaflets on a labor contract ballot at the Everett factory.

Boeing and the union that represents its 23,000 engineers are locked in a labor contract dispute. Boeing is currently beset by battery problems on its Dreamliner jets.

The new contract proposed by Boeing is now being voted on by union members. The ballots mailed on February 5 recommend members reject the "best and final" contract that Boeing offered on January 17. The votes will be tallied on February 19.

The Society of Professional Engineering Employees in Aerospace (SPEEA) said late on Wednesday that the complaint filed with the labor relations board include reports of managers holding mandatory meetings with employees to "interrogate and intimidate them regarding the current contract votes."

"We are extremely disappointed in the company's misconduct," Ray Goforth, SPEEA executive director, said in a statement.

Boeing's offer extends the terms of the previous contract for another four years and includes 5 percent annual pay raises for professional and technical workers.

However, the union has balked at a Boeing contract that it says would cut the growth rate of compensation of professional and technical employees. Boeing says its latest offer is much improved over its initial proposal and reflects a tough competitive environment.

Boeing officials could not immediately be reached for comment by Reuters outside of regular U.S. business hours.

In October, SPEEA accused the airplane maker of videotaping members marching for contract talks and of seizing members' cameras and deleting photos. The labor relations board is yet to give a verdict on the complaint.

(Reporting by Sakthi Prasad in Bangalore; Editing by Michael Perry)