Which Christian religion considers the shaving of one's beard a severe sin?

"There are quite a few scripture that mention beards in the Bible. An example would be Psalm 133:1,2. An Amishman does not shave his beard after he becomes married; a long beard is the mark of an adult Amishman. Mustaches, on the other hand, have a long history of being associated with the military, and therefore are forbidden among the Amish people."

http://www.800padutch.com/amishpeople.shtml

Many western Christian faiths encourage the growth of beards, such as Mennonites, Anabaptists and Amish. The Eastern Christian faiths also encourage beard growth at least among the clergy. I could find no Christian sect which had Commandment #11, "Thou shall not shave" in their Catechism. It seems more of a subcultural norm than a theological mandate. Beards/religion is nicely covered in the Wikipedia entry for Beards.

https://en.wikipedia.org/wiki/Beards

Unmarried Amish men are required to shave their beards.

Don't foerget the Old Believers of Russia.

https://en.wikipedia.org/wiki/Old_Believers