Boeing and SPEEA are in the midst of trying to negotiate a new contract with Boeing just yesterday saying that they will seek federal mediation in the contract negotiations. However in recent weeks it has become very noticeable that the 787s that are on the flightline aren't flying that much despite many of these airplanes being outside for weeks and many that should have taken their B-1 flights have not made their first flight.
SPEEA has encouraged its members to take workplace actions such as slow downs and rejection of voluntary overtime. These workplace actions may be the reason why there has been a drop off in flight and ground testing activity on the deliverable 787s at Everett. I count at least 6 aircraft that haven't had any recent flight activity or has been out on the flightline for some time but have yet to take a first flight (this includes one aircraft in the paint hangar as of this morning). Boeing engineers are needed not just for design and production of the aircraft but are also for the pre-delivery ground and flight testing to resolve issues prior to delivery to the customer.
These workplace actions won't be enough to stop production and delivery but can significantly slow the delivery process down. SPEEA members hasn't taken a vote, yet, on whether to authorize a strike but with the current contract expired and the negotiations deadlocked, it may not be too long before that happens. If and when that happens then it is up to the leadership at SPEEA to call a strike and then all bet are off and production at Boeing's commercial aircraft plants will drastically slow down.
In the event of a strike by SPEEA, Boeing will probably turn to management engineers to fill the void but that will probably still won't be enough. IAM751 has a current contract with Boeing but I'm not sure if they would honor a picket line by SPEEA or not. As mentioned earlier, Boeing is asking for federal mediation in the contract talks so we'll have to see how that plays out.