Is it legal for an employer to change your health insurance without your knowledge?

Yes, legal in GA. Employer does not need your consent. Employers offer the insurance, they may change any way that they wish, so long as the policy complies with the law. As to the $6000 deduct-able, I suspect that is legal, but I do not know. Like any other employment benefit issue, if you do not like this, your remedy is to find another job. The new plan must be legal - you are on your own to figure that one out. Many plans were declared illegal because they were sham policies - like no hospital coverage.

The insurance laws are changing dramatically, thanks to "Obamacare" It is most likely that your employer had no choice. Case in point, after years of insurance, my office received a notice that my office insurance was being cancelled in its entirety as of June.... not because I didn't pay, but because they (the insurance company) decided to change the policy.

Your pay stub reflects all the charges against the pay earned. You can decline the insurance and go with your spouse's carrier. Otherwise, you can purchase your own policy.