He put me on an action plan 1.5 weeks ago for class management. It is through next winter. Yesterday, the union rep said she couldn't understand why because it didn't sound like I was having problems that are not typical for young, first year teachers.
I'm not sure if he is trying to get rid of you, but it is becoming more common place for first year teachers to be put on an action plan.
Back in the olden days of teaching (when there were jobs available), there was a sliding scale. So the expectations for first year teachers was a little different for 35 year vets. That is not the case anymore. Everyone is held to the same standards (at least in my district and many neighboring districts). So a first year teacher will most likely be deemed a basic teacher and receive an improvement plan.
Since you're a new teacher, the principal is probably just trying to give you specific advice in order to make you more effective. All new teachers have "improvement plans" in my school--it's required as part of their certification process. They choose their areas of weakness, though, and a mentor and administrator need to approve the timeline/action plan, though.