“I ask you to not sacrifice the chance to safe our future collectively, due to the frustrations of the previous,” mentioned Mr Ortberg in his message to employees.
“Working collectively, I do know that we will get again on observe, however a strike would put our shared restoration in jeopardy”.
The present contract between Boeing and the unions was reached in 2008 after an eight-week strike.
In 2014, the 2 sides agreed to increase the deal, which is because of expire at midnight on Thursday.
It comes as the corporate faces deepening monetary losses and continues to wrestle to restore its popularity following latest incidents and two deadly accidents 5 years in the past.