But Ms Morgan told delegates the government's plans would improve the education system in England.
"I want to be clear [...] there is no reverse gear when it comes to our education reforms."
Ms Morgan also accused the NASUWT of peddling too much negative comment about the state of the profession, teacher retention and recruitment.
"If I were a young person making a decision about my future career and I saw some of the language coming out from the NASUWT as well as some of the other unions, would I want to become a teacher?
"If I read about a profession 'standing on the precipice of a crisis', would I consider a life in teaching? - no I would not."
Ms Morgan went on: "The teaching unions have a choice - spend the next four years doing battle with us and doing down the profession they represent in the process, or stepping up, seizing the opportunities and promise offered by the White Paper and helping us to shape the future of the education system."