There is a huge difference in the way the (pilots)unions in the OneWorld Alliance view the whole merger/joint venture development as opposed to the unions in the Skyteam Alliance. Just look at the current opposition from the AA pilots against the JV with BA.
This can be of great influence, as the previous poster also indicates. You need to have the support of the employees if you want to go down this path.
The brandnew JV between AF/KLM/Delta over the north atlantic will be a great success and is fully supported by the pilots.