I work in an office which operates very lean. My employer expects all work to be done, however, he does not want to pay overtime. He had us sign a paper saying we will not work overtime unless authorized. When you ask for authorization because of work load, you are turned down. So we come in on our own time to keep up on the work and they say "You know I'm not asking you to come in and work". If we don't come in and keep up on our work they call you in the office and tell you the owner is concerned you can't keep up on your work.

They can certainly discipline you for not following company procedures. Assuming you are a nonexempt employee (basically, hourly-paid, but not necessarily), however, they cannot do so by not paying you. For the overtime due you for hours you worked in the past, you can file a claim with the Division of Labor Standards Enforcement. In the future, I would not work it. Period. And I'd start looking for another position. They expect the work done, but they don't want to pay for it. :(