Denial marriage because one takes communion and the other does not, it is believed in Biblical terms the couple would be "unequally yoked"

In the Bible 2 Corinthians 6:14 says:
"Be ye not unequally yoked together with unbelievers: for what fellowship hath righteousness with unrighteousness? And what communion hath light with darkness?" (KJV)

http://www.belfasttelegraph.co.uk/news/local-national/article3429527.ece

There are Christian unbelievers?

Interesting, I remember reading a post on an Arabic forum mentioning 'Christian Unbelievers' and was wondering what that meant.

Two phrases that explained who they were, but it still wasn't clear: They deny their prophets, and they take the righteous as enemies.

Interesting!
I'm wondering, what's the proper definition of "Christian unbelievers"?