From the union...

"Before we get into anything else, we want to again discuss the possibility of 15.G.4. Every First Officer who meets the FAR minimums to be Captain has the potential to be displaced to Captain either on this bid or the next one, so it's critical you pay close attention.

Here's how it will work:

The Company will award vacancies by via the normal process: preference first, in seniority order.
Unfilled Captain vacancies will be noted (if insufficient preference bids).
Proffers to displace will then be considered for the unfilled Captain vacancies, in seniority order (from top to bottom). Proffers to displace do not incur a training freeze (seatlock) nor will they incur any sort of flow freeze or flow lock.
Once/If all proffers to displace are exhausted and unfilled vacancies remain, the parties will tally the number of unfilled vacancies. Starting at the bottom of the seniority list, the parties will identify a sufficient number of the most junior qualified pilots (working from most junior to most senior) and place them into a pool. The parties will then turn to the most senior pilot in this pool and involuntarily assign him/her to any position that their seniority can hold while respecting displacement preferences."