How to ensure that a civil union can be treated as a marriage for federal tax purposes

There are a couple people out there who believe that marriage should not be regulated by the state. These people want to get the government out of marriage, and let the government regulate civil unions instead. I sympathize with these people, and want to start a movement to make my state only give out civil unions rather than marriages. This includes hetrosexual relationships as well.

Howver, I know that if my state does this, there is a chance that the federal government may deny beniefts to hetrosexual civil unions. So I want to know how to ensure that the federal government treat a hetrosexual civil union as a marriage for tax purposes. Can you help me out? Or not?