hired but lower pay rate

What is the name of your state (only U.S. law)? California.
I worked in an extrusion company for 6 months as a temporary employee from the agency. I receive $11/hr. Last week, my employer offered to make me a permanent employee. I was so excited but when I saw the offer paper, they will just give me $9/hr and be on probation for 90 days to enjoy the benefits. I was hesitant to accept the offer but the HR told me that its accept the offer or be terminated. I didnt feel too welcome and it seems that it was unfairly based offer since they lowered my salary. Is there any legal law violated by my company in imposing that to me?What is the name of your state (only U.S. law)?

It is not unusual for you to get a higher rate from an agency than from the employer. I'll bet you aren't getting any benefits through the agency, and even if there were no other differences, benefits can definitely cost the employer $2/hour.

Perfectly legal.

Not even remotely illegal. You get a higher rate from the agency because you aren't eligible for benefits from the client company.

As long as you are being offered minimum wage or better, it's legal.