I work as a diesel technician in Tenessee. We are paid commission-only based on Blue-book hours for each job or repair we perform.
When there is no work, we are required to stay on the premises (Although we are not performing a task) and are not compensated for these hours.
Is the employer required to give SOME compensation, since they require us to be present?
Can the employer make the decision to leave without negative consequences?

Tennessee follows federal law for its Labor Laws.

Labor Laws Regarding Commission Only Jobs | eHow.com

I will say the job as described is the same for many people, insurance agents, tattoo artists and more.

If you leave and someone drives in, who is going to fix it THEN.

The issue I see is, how often is there no work ? Are you discussing a hour or two here and there, or is business so bad, there is seldom work?

Work is steady most of the time, although it seems there is always a terribly slow spell on Election year. Lately it has been only a couple of hours at a time, but at times, as much as 5 hours of boring down-time.