Teachers rights

Yesterday at my class in high school the students worked on paper that was to be turned in at the end of the period. Experience has taught me that some students will not do the work and not turn in the paper and later tell the teacher that they didn't know they were supposed to turn it in. Thus I stand by the door reminding everyone to turn in their papers. While I was saying lets see your papers, lets see your papers I was reminded of those old WW 2 movies where the Gestapo is always asking for papers so I said, I sound like the border patrol. Within minutes the assistant principal was at my door saying he got a complaint that I was talking politics. Someone apparently thought I was referring to the US-Mexico border. The First Amendment right of teachers is in jeopardy.