Can employer require extra duties and attendance @ work without pay, and force dispatch drivers paid by % only in Texas?

My terminal manager requires drivers to report 2-3 hours before load times without pay, attend safety meetings one time a month on saturday mornings without pay, and force drivers to accept loads or threaten them with a write up for refusing a load. As employees, we are paid a % of the adjusted gross revenue of the load, and we receive an hourly rate for non-revenue duties. What legal rights, if any, do we as drivers have with regards to compensation for such extra duties, and what options do we have when we do not want to accept a load? Some drivers consistently turn down loads that don;t pay much without any consequence. Is it possible for my employer to force dispatch drivers? Are there any legal remedies available for commercial drivers in such instances?