Disloyal or Unloyal?

Disloyal and unloyal both describe a failure to show loyalty. Many believe that unloyal is wrong because disloyal is so much more common. (Of note, Google will search for disloyal if you type unloyal, but it will not search for unloyal if you type disloyal.)

Examples:
  • There's the most resistance to an actor singing. It's like I'm being disloyal to my industry. (Kevin Bacon)
  • Normally when most people lose a pet, they get another and keep going on. But it just felt wrong to me; I felt unloyal. (Robert Crais)

Use Disloyal

Although unloyal is acceptable, disloyal is universally preferred.

(See evidence of this claim in Google's Ngram Viewer.)