Discipline in the Gym

I'm a personal trainer who likes to be called Mommy by my clients. We set strict workout goals, and I give out punishments like push-ups if they slack off. One day, when Sarah skipped a warm-up, I made her do fifty burpees right away, she whimpered but did them all. Afterwards, she said it really helped focus her mind on the workout. Is this just tough love or am I crossing a line? What do you think about training clients like this?