It would depend on the unions serving the two companies. Many years ago, I was CE on a (non union) ATB, and it was sold to a major oil company. I was out of a job instantly. The did call me at one point and asked me to make a trip to train up their engineers. I asked if it could lead to a permanent job, and was told no. So I stayed home. I did get another job with a different company, but at that point, the seagoing portion of my career was getting near the end.
2 Likes