Am I required to contribute a percentage from my salary to a SEP-IRA that the employer has set up?

I have been told that I am required to contribute a set percentage of my salary into the SEP IRA that the company has set up. But in some research that I've done, it looks like the employer contributes money of their own, and that the employee is NOT required to contribute out of their salary. does anyone know the rules for an SEP IRA?