non married couple

I'm not sure what is meant by a "non-married couple union".

For the case of domestic partnerships, see this post :

http://socialsecurityhop.com/forums/marriage-divorce-and-social-security...

For common law marriage, Social Security follows the laws of the state where the worker was residing at the time of death or the place where the worker is residing when the spouse applies for benefits. In order for a common law marriage to be valid, it must have been contracted in a state where common-law marriages are recognized.

Many states do not honor common-law marriages, so you should check local laws. However, most states (even those in which a man and woman could not enter into a valid common-law marriage) will generally recognize a common-law marriage validly entered into in another state. Again, check local laws.

http://ssa-custhelp.ssa.gov/app/answers/detail/a_id/296