Rejection of the proposed contract came on the same day as Boeing reported a net loss of $6 billion in the third quarter.

Boeing shares fell 2.7% in U.S. pre-market trading on Thursday after workers voted to extend a nearly six-week-old strike, throwing fresh uncertainty over the company's efforts to stabilize finances and restore its battered image.

The vote comes more than a month after 33,000 union members overwhelmingly rejected a negotiated offer and walked off the job on Sept. 13.